Map multiple input channels to tracks

Well, the first thing you do is go to Edit/Preferences/Audio Hardware and make sure you have selected the right Device Type/Driver.  In this case it will likely be ASIO with some reference to Steinberg.

Then go to File/New/Multitrack Session and create a session.  In the Input selection box (the one marked with a right-facing arrow) it'll probably say either "None" or something like "Default Stereo Input".  Click on the Input box for the first channel, select Mono, then pick the first of your Steinberg inputs--I can't give you the exact wording since every interface is a bit different.  Repeat this in track two with the second Steinberg input and so on.  Once you've done this, click the little red "R" on each track you want to record in to arm it for recording when you hit the main record button.

A couple of hints:

First, to avoid having to do this for every recording, once you have your session set up properly, save it as a template.  (File/Export/Session as Template) so you can just open your standard work space every time.

Second, if there's any chance you may want to do multiple takes, when you make your Session Template, repeat the channel assignments a few times--so tracks 4, 5 and 6 are repeats of Steinberg channels 1, 2 and 3 and so on.  No problem if they're not used (just don't arm them for recording until you need them) but a potential time saver later.

Hope this helps.