Displacements are created by selecting the faces you want to turn into "terrain" and going to the "displacement" tab in the texture window. Select "create" and choose one of 3 of the displacement powers available. 2 and 3 are best, try to avoid 4 as it's difficult to work with.
If this is your first time logging in after the migration (Feb 8, 2022), you must reset your password to log in. Follow this guide if you're having trouble