Sculpting tool not doing anything

Hey everyone.

I’m very new to UE but from all the tutorials ive watched its my understanding that when using the sculpting tool a left click should be raising the surface of the landscape. For some reason this doesn’t do a thing for me. When i click down the sculpting tool goes astray and slides all over the place but no changes are made to the height map. Ive tired lowering my render settings and nothing has worked. Anyone else experience this issue or know a work around?

system:
mac Os 10.12 Sierra late (2013 trashcan)
64 gb Ram
AMD FirePro D500

thanks!