O.K., I know collision, such as fighting or talking with people, but how do I make it so that if I were to run into, say, a building (screenshot) I wouldn't run through/over it? Is there any solution?

im just starting with smilebasic today myself, but does your bg objects have bounding boxes? im assuming your player will, lets say your bg object does, and that you bg objects bounding box would be checking y+1(bbox_bottom) and your player would be checking y-1(bbox_top). anyways if these two are true i would set your vspeed to 0, hspeed dont change and add an else statement for moving down

so the logic would be if player bbox_top and bbox_bottom wall and up and !down, vspeed equal 0 else if down, vspeed equals -2 or whatever

The higher a sprite number, the more on top it's going to be.