what does changing back to master branch mean? how does one do that ?

I wanted to work on it after 6 months and it asked for a bunch of updates. I did git stash and git stash pop etc since it would not let me update otherwise.
however, after updating the main system, there were updates to MMM NOAA and MMM-singlestock. after I did that, the system didn’t work at all.
what should I load here (config.js file, any code etc? ) to get some help on this.
I deleted MMM-SingleStock but it doesn’t changes anything.
upon launching the system it gives a bunch of msgs and then goes to launching application, but the computer just freezes and I have to start by unplugging it.
here is a snap shot of the msgs I get.

Please help.