Welcome to the site!
Iwaku can seem a little big and daunting at first but I think that it's easy to get a hang out (but if you need any help, feel free to ask!).
The layout is about as sensible as we could get with as many sections as we have!
You've got "announcements/events" followed by "Site Orientation (with welcomes and help desk)" then on to the headliner items "Roleplay Out of Character Sections" and then "Roleplay In Character Sections".
The Roleplay Realms are each one roleplay that won a contest here to get their own subforum.
After that, you've got your relaxing areas where members can go to talk out of character, trade art, etc.
Some places to practice writing with prompts and read guides about writing.
And finally, the archives where old roleplays and threads go to die!
I hope that that helps a bit in thinking about where to find something, on the main page at least!