Usually smoked off glass. You can smoke it off foil too. Apparently can be mixed with vape juice and vaped. Years ago I put chunks of meth into a vape pen meant for smoking weed/wax and smoked it while playing pool in a pool hall (not a good way to do it but it does work, I just did it to prank my friend, "hey man you know what that smell is?").
But this new cartel meth going around doesn't smoke well, the effect being jittery and edgy. Best way to use it is just eat a chunk of it, .1g (100mg) or more (depending on your tolerance).