first you need to make a floor (draw one in paint or something) now to make the actor stop when he toushes the flooe youll need to make an event : player collides with floor phsycal responce leave the top 2 neumbers clear and set the 3'rd one down to 0 (this means he wont bounce.
to make your actor jump there are two options i know 1) player key down Space script editor [yvelocity = + 5;] or [y = y - 5;] that means on the
Y axis he will go up (hot tip- enable gravity so he comes back down lol)