Creating a jump pad is very easy. First of all we need a platform in our map the player can't reach with normal jumps. I've built one in the second room. You can use the map at the bottom of this tutorial if you want to use mine or build one by yourself. I've also put the rocket launcher there so the player receives a small reward when he jumps up there.
Now create a new six-edged brush. For that draw a new brush and go to Brush/6 sided in the bar above the windows or press Ctrl+6.
But that looks ugly without a good-looking jump pad texture. Go to textures/sfx and search for a nice texture you want to use. I'll take the diamond2cjump pad texture because it is compatible to our floor texture. Now adjust it by hand or via the fit button in the surface inspector (s):
Select the whole jump pad again, copy it (spacebar) and put it above the jump pad brush. Now go to textures/common/trigger:
Leave it selected, press the right mouse button in the top view and select trigger/trigger_push. In the trigger category you find all trigger functions a trigger can be converted to. Always use the trigger texture on a trigger. It's easier for you to differ it from normal brushes. After the convertion, deselect the trigger, use the right mouse button again and place a target_position (green box) above the trigger. Also higher the target a bit and move it nearer the platform:
Deselect everything. First select the trigger then the target_position and press Ctrl+k. Now a green line should appear.
This will be the way the player will jump when he touches the trigger. The higher you put the target_position the higher the player will "fly".
Here you can get the maps for this tutorial (place it into baseq3/maps):