How to select mutiple songs from iTunes on Mac with Windows keyboard?
To select a continuous grouping you select the first one and then press and hold the Shift key, then click the last one in the group.  To select a random grouping you select the first one and then press and hold the Command ⌘ key (on a Mac keyboard) or Windows key (on a Windows keyboard on a Mac), then click the next one and so on until all are selected.  You can let up on the Command ⌘ key or Windows key in-between selecting however make sure you press it before selecting the next one or it will break the grouping and you'd have to start over.

You can deselect by pressing the Command ⌘ key or Windows key, then click the one(s) to be removed.