how do I open multiple windows on the mac?

If you'd like them viewable at the same time, drag any corner or edge to resize the window and drag it to the side using the top bar of the screen. Now do the same for the other app.

In the Finder?

File>New Finder WIndow or command - n.

Matt

Yes, but if I do that, each window cuts off part of what would be on the screen.