Other (perhaps,new) maps and units

Sirs, i would like to ask if there's someone who can help me, as im a newbie, in playing (new) other maps other than the default world map and its variations-eurasia, eu+, etc... i wanted to try other maps but when i joined i realized that there are new units or my strategy aren't fitted as the map doesnt have the units which i have for my upgrades..

perhaps, a request of a summary of maps, details of the map (a history or how is it played) and its units..

That because those are custom maps

there is no real guide for those