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.
You can move multiple layers at once by holding down ⇧ and selecting the layers individually before dragging.
If you prefer, you can also group layers together in the Layer List (or pressing ⌘G) before moving them as a unit.
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