Download Demonbuddy to your desktop.
Make new folders inside called "Profiles" and "Plugins" (makes finding things easier)
Download the Trinity Plugin (version 1.7.2.11) into your Plugins folder.
Download the Trinity Routine (not the plugin, the routine) into your Routines folder in Demonbuddy.
Download the "A3 by rrrix" Profile into your Profiles folder.
Download QuestTools into your Plugins folder.
Start D3 and log into your character you want to bot.
Once you do that, load up Demonbuddy.
Enter the key or w/e they give you for the free pass to start it up.
Click the Plugins Tab in the Demonbuddy User Interface.
Click the little box next to Trinity to Enable it.
Don't click the QuestTools one (it needs to be there but you don't need it clicked).
Make sure you have the Kill Azmo Quest (not chosen, just make sure you've done it already).
Click the Down Arrow by the Settings Tab in the Main Section of the Demonbuddy User Interface, then click Bot.
On the right side it will say Monster Power, choose the one you want by moving the slider.
Hit Save and Close.
Hit Start, when it asks you to pick a Combat Routine, scroll down to Trinity and click it.
You're now farming A3 Inferno at the MP level of your choice.
Welcome to Demonbuddy.
*EDIT*
Once you're running, read up in the threads for Trinity to see how changing item scores and loot are done so you don't keep stuff you don't want. I also suggest reading the Reducing CPU Usage link in my signature. It will help will efficiency and overall xp, gold, and items per hour drops.