This tutorial will teach you how to create an area of your map have lower gravity than the rest of your map.

1- Firstly move to the doorway (entrance) of your room that you want to have low gravity *screen1*

2- Then Create two blocks with the trigger texture the hight of your doorway and half the width of your doorway. *screen2*

3- Next place the two trigger textured blocks into the doorway. *screen3*

4- Select the block that if your player walks into this room he will wal through this one first *screen4*

5- press ctrl+t to tie this block to an entity, tie this to trigger_gravity. Then leave all the properties the same on this block.

6- After that tie the block that your player will walk through last to trigger_gravity aswell. You need to change one of the properties for this and its the bottom one the (gravity 1-0) 1 is default gravity so change the number to fit your liking try 0.5.

well thats about it test your map and adjust it untill you like it.
If you have any preoblems just contact me.