As with all Xiaomi phones, there is no manual. However, the A1 is a plain-vanilla Android phone. To see settings for the SIM fo through the settings menu and look for network settings and connections.
I was home in Arizona this summer with my A1. I used AT&T. Do mind that, unless you're in a major city you likely won't have LTE as the phone is made for Asia. Otherwise it should be a great phone. My A1 doesn't disappoint.