choose a point within range a 20ft sphere centered on the point is either compressed or expanded your choice 

compressed 

while inside the sphere a creature can expend 10ft of movement to teleport to a point within the sphere.if a ranged attack would pass through the sphere can treated as if it originated at any point within the sphere.

expanded 

the area becomes difficult terrain and any ranged attack passing through the sphere is made at disadvantage.

at higher levels

when cast with a 4th level or higher spell slot the affected area increases by 10ft for every level beyond 3rd

in addition a secondary benifit is gained based of function if the spell is cast at least 5th level 

compressed

the movement expended to teleport is reduced to 5ft 

expanded 

the area becomes greater difficult terrain