There’s very detailed info here: https://www.avid.com/P2/
Make sure to read it thoroughly.
In short, under the File menu, you have an “Import P2” option, with two tabs, “Import Clips” and “Import Media”. You’ll have to first import the clips (metadata) into a bin, then either choose to import media (natively), or Transcode/consolidate to a resolution of your choice.
After that, you’re editing.
I’ve often read that editing 720 on MC is not a joy per se, but I can’t really say, since I’ve only done 1080 P2.
Also, you might want to know about the existence of Raylight MXFX, application that lets you convert MXF files from and into various formats and framerates.