Have you tried those?
Overdubbing needs to be on, or Audacity won’t send out the song while recording…
And I suppose Audacity will send playback to outputs one and two by default, but I don’t know, as I’ve never tried the US1800 with Audacity. So you might need to try outputs 3 and 4 too.
BTW, the Tascam is one of the easiest devices in it’s class. The software setup only sets sampling rate and spdif in/out. No software mixer, no routing. All input channels get sent to monitoring at the same level. No choice, no gain controls. One weak point is that it only has 44 dB gain on the mic inputs, which is not enough for an SM57. Unless you’re a real loud singer.
I think for Protools and Cubase you need to set the master bus to the appropriate outputs to get sound. I don’t know the routing matrix in PT Free, but usually in a DAW, you need to set that too, routing each input channel to the master bus. And of course, you need to slide the faders in the mixer up AND in the master channel.
DAW’s require setting up (and saving) a project before doing anything else. That requires reading the manual and thinking about stuff like sample rate. It’s not something you learn by watching a 5 min. Youtube vid.
The only daw that is easier, is Presonus Studio One 3, because it comes with templates for the most popular projects. One of those is a 16-track rock song, fi. It comes completely labeled, with even the faders set to probably good levels for drums, guitar and so on. That gets you going a lot faster.
One limitation of Protools free you need to know about, is that you can’t open it’s projects in other Protools versions. Seems like a serious shortcoming to me if you are thinking of passing the project to someone else to continue mixing/mastering your song.
But Audacity should do fine to learn the basics…