I'll do you a quick step by step guide and then give some tips:
1:
Download Trinity Plugin and TrinityRoutine
2: Open your Demonbuddy folder and extract (you will need a program like winrar) the Trinity file into your plugins folder and the Routine into the Routine folder.
3: Download a profile, highly recommend both
Fallen Dev's Act 1 Profile and
Kunstprodukt's Act 2 Profile
4: Start Diablo and then Demonbuddy. Open the
Plugins tab and enable Trinity.
5: Back on the main tab you have a down arrow next to "Settings," press that. In there you have a few options, you can ignore the checkboxes under "looting" as Trinity has the same options.
6: Now to Plugins again, mark Trinity and press "Config." In there you can play around with even more settings.
You're now 100% done with the bot. Just load a profile and hit start.
General tips and my opinions:
I'm not going to explain everything but leave you to experiment with the other options in there. Try different settings and profiles, what works for me might not be the best for you.
If you run a Barbarian the go with the Act 2 profile I linked and check "Ignore Elite/Rare/Unique packs" in Trinity. Change the minimum trash mob pack size to something around 7, i run 9.
Run Act 1 if: You are a Archon Wizard/Long Range WD/DH
Run Act 2 if: You are a Barb/CM Wizard/CoB or D0G WD
Run Act 3 if: You can't handle MP1+ (HC usually)
If you get the error "Authentication failed" after Demonbuddy was shut off then go to
Log On - Buddy Auth Portal and kill the session to start a new one, or wait for it to kill itself.
Feel free to ask questions, I'll check back here tomorrow. Good Luck!