Sure, no problem
Alright, first find a song you want from the link I provided above. Lets say you want Erotomania. Go through the list of songs on ultimate guitar until you find a guitar pro tab for Erotomania... click the link
https://www.ultimate-guitar.com/tabs/d/dream_theater/erotomania_ver2_guitar_pro.htmOn that page, you'll see a few different things... it has the file size ( 59 Kb) as well as the instruments tabbed out in the file (guitar #1, guitar #2, guitar #3, bass, keyboard #1, keyboard #2). Go toward the bottom of the page and inbetween a few ads there is a button that says "Download "Erotomania" Guitar Pro Tab". Click it, and save the file to somewhere on your hard drive.
Once that finishes, open up Tux Guitar. Go to the top of the page and click "File", then click "Open". Navigate to the folder with the guitar pro tab file, and select it. Once it loads, you'll see the score infront of you. Towards the bottom of the screen is the selection of instruments... most of them are labeled by what instrument they are or who plays them. In this case, click the bass (John Myung). From here on out, it should be self explanatory... just read and play! You can also have the computer play MIDI versions of the tab by clicking the "play" icon near the top of the program in the toolbar.
I hope that helps, let me know if you need anymore help and I'll try my best!