well walking is simple, if you want to walk him back a forth.
set the character AIMAIN, to follow, or if you want him to shoot you aswell set it to pace. place a waypoint path.
find the waypoint icon in the tool bar, click to start the path, to make another just hold shift and click over the previous one.
smoke out a bath tub, well i guess its a decal. in entities, in generiac, look for decals or something. there is a list look for smoke then place it over the bath tub.
stacking objscts, well place the first object, say a box, to place on on just hit enter, when the second box icon is over the previoulsy placed one.
hope this helps
sorry if all my post annoyed anyone, didn't know i was a hassle