Select an object under an object

"cannot figure out how to select a shape underneath another shape"

Rather than click-to-select, drag a rectangle from left to right that encloses only the thing you want to select:

If the (red) drag rectangle starts outside all the other stuff and encloses just the dog, as shown, you’re done.

Note that dragging the rectangle right-to-left selects everything the (green) rectangle touches, which is sometimes what you want but more often leads to heartache & confusion.