how to delete multiple songs at the same time

Highlight the multiple songs as follows:

• To highlight a range of songs, click the first, hold Shift, and click the last.
• To highlight a bunch of selected songs that are not in order, hold the CTRL (Windows) or COMMAND (Mac) key and click each one.
• To highlight all the songs in the view, click any one, and then CTRL-A or COMMAND-A.

Then hit Delete (if you are removing from a playlist) or Option-Delete to remove them from your library entirely.