To move a layer, simply click and drag it. If you want to restrict movement to a particular axis, hold ⇧ as you drag.
To move a layer that’s underneath another layer, make sure you’ve selected it, hold ⌘+⌥, and then click and drag anywhere on the Canvas.
Tip: The Mac app automatically aligns the layer(s) you’re moving to adjacent ones. If this doesn’t happen, check that guides are enabled in View > Canvas > Show All Guides