This is my U shape:
And this is how it should be:
It should be filled:
I tried in edit mode to select with B some of the faces then i did in the menu under Extrude: Make Edge/Face but it didn't fill anything and not the whole U shape.
This is my U shape:
And this is how it should be:
It should be filled:
I tried in edit mode to select with B some of the faces then i did in the menu under Extrude: Make Edge/Face but it didn't fill anything and not the whole U shape.
not sure if I missed something but have you tried classic F key to fill faces? Like
edit:
the above is the simplest, but gives you N-gons.
To fill with better topology, try ALTV:
Then, if you need quads, simply convert with ALTJ:
edit2:
cegaton commented about another smart tool, "bridge edge loops"
he's right, so you can also use that like this (note I used it before filling the side faces, otherwise it gave an error):
and you get immediately