As a member of the CEP 2.x team, I remember going through a learning curve initially, which pays off over time.
I’d recommend two complementary approaches: Story-Driven and Familiarisation.
Story-Driven ignores CEP2.x until your story needs something - a well, perhaps, or a goblin.
Chances are that CEP2 has variants of both.
We try to organise creature and placeable appearances in a hierarchy that makes things reasonably easy to find. Editing the appearance, typing “w” or “g” then scrolling will soon find wells or goblins.
For convenience, some appearances are grouped in categories - “Farm”, for example - which can make some things harder to find. Extract appearance.2da and placeables.2da so that you can text-search them. That way, you don’t need to know the taxonomy.
Familarisation involves scrolling through all the content just to see what’s there. For example, if you edit a creature appearance in the toolset, you can preview them all very quickly using down-arrow:
When I see an especially cool one, I save a copy in an inaccessible area of my module, which holds nice stuff that might conceivably be useful one day.
Familiarisation with the classification can come from browsing the 2da files to see how things are organised.
Much the same applies to other CEP 2.x content, though the creatures and placeables are the most daunting - more choice means more effort, unfortunately.
For example, tilesets can be browsed by creating an area for each option on the dropdown, then placing some tiles (Familiarisation) or you can just wait until you need a swamp (Story Driven) then text-search the tileset manual.