Hi,
The best way to get your teeth into fusion is check out RULE #0, 1 & 2 pinned to the top of the forum. They revolve
around reading the Docs, doing the embedded tutorials and getting stuck into the Self Paced Learning. Time spent
doing this is NEVER wasted. Then check out the AutoDesk Fusion YouTube Channel. All sorts of good stuff at all
levels. AutoDesk University is also good.
In terms of fixing your floor in the enclosure, you can do it a couple of ways. If the sketch is exactly the correct
shape just not in the plane you want it then you can do an extrusion but instead of from the profile plane, extrude
from an Offset or an Object.

The other way you might be able to do this is with the Press Pull command, where you literally select the face and
pull or push it up or down.

Try those and see what you get.
Cheers
Andrew