Well, you need two things
1. A gravity based system(if an object goes up, it must fall again)
2. A collision system(otherwise your player will fall through the floor)
set up the gravity for your player and make sure there is a collision system between your player and the ground. then, it is simply a matter of propelling your object into the air, something a bit like this:
`begin loop
Do
`begin the players jump
if spacekey()=1 and PlayerJumped=0
PlayerYPosition#=PlayerYPosition#+1
PlayerJumped=1 `this variable is so that the player doesn't keep jumping for ever,like a double jump etc.
JumpStatus=10 `this variable is to store the status of the jump
endif
`during the jump
if JumpStatus>0
PlayerYPosition#=PlayerYPosition#+1
JumpStatus=JumpStatus-1
endif
`end the jump and reset the jumped variable
if JumpStatus=0
PlayerJumped=0
endif
`position object in the new position
position object 1,PlayerXPosition#,PlayerYPosition#,PlayerZPosition#
`update screen and loop
sync
loop
you would also need to include the JumpStatus variable in your gravity system to make sure that the player wasn't pulled back down every time The player jumped higher.
