MCSMaster & Co. Foundry Metal Gallery Wall Frame, Black, 16 x 24 in without mat

Can I use the frame without the glass?

What's the best way to hang this? the built in saw tooth hangers don't hook onto some picture hangers (45 degree nail + hook) i got from target

Can I frame a 3/8 inch thick foam board in this frame?

What does “comes without mat” mean?