I need some help please

Hi,
Sorry to hear you're having trouble. But when it "clicks", you'll probably enjoy it more than all those other games.

There is a lot of debate and threads about the "best" way to play, and doubtless the old hands know the best references to point you to for advice and strategy guides. The sticky "Wiki/Guide/Faq" thread is an obvious choice, although it can be hard going to read all four pages.
But to help with your immediate problems:
- the tasks given in the scenarios usually do NOT guide you forwards in building a good network. The locations are chosen randomly from a fixed list, and rarely point to good locations to cover. And even when the locations are good, it may not be a good idea to cover them with a single line. Mostly, just build a couple of bus stops covering the required locations, add a vehicle, activate the line (I often forget to do this), get the credit for completing the task - and then delete the line! Reassign the vehicle to another overloaded route, or store it in your depot until the next task comes along. The task routes are almost always very bad for profit generation, so don't ever feel you must retain the requested route. If passenger numbers are low, then absolutely you should dump it in favour of more lucrative positions. Ideally you'll want to see more people waiting than your vehicles can carry. Don't be scared of angry red faces from waiting passengers - it's a compliment that your network is appealing - you just need to resolve a bottleneck by adding more vehicles to a line.
- following on from that, don't wait for the tasks to appear before building lines. Have a look around each map, find the best places to cover (see below) and start building the network you think is suitable...
- passengers pay once per mode of transport used. So if you have all bus lines, you will get one fare per passenger journey, regardless of how often that passenger changes bus lines. But if the passenger uses a bus and a tram to make his journey, you will get one bus fare AND one tram fare. So, planning a network to use multiple types of transport is best for getting income.
- your network MUST cover a good SOURCE of passengers - homes like high density apartment buildings are excellent. Your network must connect them to places that people want to go to - large office buildings and department stores seem to work best, although "leisure" (like stadiums, theatres and libraries) and factories are also worth covering. Railway stations are classed as leisure, but I also find they can be one of the biggest sources of passengers too. It's generally a good idea to start your first line from the biggest train station in the town.
- shorter routes are less likely to cover enough passenger source or destination, so they will work worse. You are better off having one long snake of a line, or a big loop, than lots of little local lines. If the local lines link together, it can work, although you'll get lots of waiting passengers at the transfer points, making their journeys slow, and they'll be unhappy about that..... Local lines of less than four or five stops probably won't work. I'd expect minimum 8, up to 10 or 12 stops to be sensible. Once a line gets to 15 or 20 stops, it starts to get too big to manage. But I have had some metro loops with 25 stops in them towards the end of scenarios.....
- buses work well in early scenarios (1920's), while trams cope with bigger passenger numbers when buses get overwhelmed. Ultimately, a metro system can handle very large numbers of passengers and generates the biggest profits. Many players use a metro for high speed connection between areas, then use buses and/or trams to collect and distribute passengers locally around each metro station. This gives wide coverage, and multiple types of transport for fares. So long as the NETWORK covers the passenger sources and destinations, all will be well. The bigger the area covered, the more passengers will use your network. If passengers can't make their entire journey using your network they won't use it at all.
- reduce stop maintenance if profits are being squeezed. This reduces the appeal of your network a bit, but I find it saves much more than it loses. You can skimp on vehicle maintenance too - vehicles will just degrade more quickly and break down more often. Again, not a killer - you can replace the worn out vehicles later when the cash is rolling in (and improve the maintenance too).
- don't be scared of the high interest loans. The lower monthly repayments can be a life saver.
- I never use ads, unless the task asks me to, or I need to boost the appeal of a particular group. Even then, 2 out of 3 scenarios complete without ever using advertising. If you place the network coverage well, the passengers will come anyway!

It's hard to give all of the advice you'll need, but I think this game suits personal style very well. There is no single perfect "formula" - from what I've seen almost anything will work - so long as the general rules on covering a passenger source and linking to a suitable destination are followed. Within that, the scope for personal choice of network layout is very wide indeed.

Hope that helps.
In hindsight, the biggest hurdle I had to overcome with CiM was the realisation that the scenario tasks were mostly just distracting wastes of time, rather than carefully chosen guidance..... Things will go much better once you see them as "do this to get that", and once done, delete it immediately, then carry on building the network you want!

While I would also say it might be best to play through the original CiM campaign scenarios first, Ulm also felt fairly simple to me and should be OK to continue with. But you'll certainly enjoy the other DLC (especially Tokyo and US Cities) more AFTER completing the original campaign. The DLC maps get much bigger, and much harder to cope with.
Once you complete a scenario in the main campaign, it unlocks for individual scenario play later.

Besides what bythelee said I can add that those four pages of Wiki/FAQ/Guide are organized in the pages below.

http://citiesinmotion.wikispaces.com/FAQ
http://citiesinmotion.wikispaces.com/Hints
http://www.cimexchange.com/index.php?/tutorials/

And its worth enforcing that you shouldn't use the missions as a guide to play. Just play and when you have the money you complete the missions. They are not what you should do to be successful as expected. They are just missions that follow a story line and you need to complete to play the campaign.

When you have being successful already and you have clear in your mind the concept of network, might be good to read this too: http://citiesinmotion.wikispaces.com/Mobility Guide

The key word is NETWORK as bythelee said so many times. Think it just like in the real world, not like Traffic Giant.

My advice is to leave the campaigns for later, sandbox is much better imo.

Don't hesitate to share whatever your problem will be. We will be happy to serve you and discuss it here. God bless!