You are not really helpful. I tried to learn. Too complicated.
then you didnt try hard enough. seriously, trade is one of the easiest things in the game, and very essential as well.
short explaination forgetting forcelimits and strategic options.
trade is the siple process of pulling money from an region to an region you want, then collect it there. you can pull an amount of trade equal to the % of trade power you have+possible modifiers. you can also collect trade from the total, which you will do automatically in your capital, equal to the % of trade power+modifiers, althoigh collecting outside your capital will have pretty large modifier ti make that less effecive most of the times. to do this you need merchants. you start with 2, but cnan gain more through decisions, NI's and idea groups. merchants give an small amount of trade power themselves as well.
the 2 main ways to get trade power are provinces and light ships. rach province you own in an trade zone gives you trade power in that trade zone, increased by trade buildings, with centers of trade and the estuaries of large rivers(i.e. the rhine in holland for estuary or paris for center of trade) which give you even more trade power.
trade ships can be used to increase trade power in all nodes that are nrxt to water. its an job you can give them, where they will patrol the waters and increas eyour power while they patrol. lowering maintenance on the fleet will decrease their effectiveness. newer models give more power.
there. the TL;DR version of trade.