Before We Start: I would like to say BACKUP YOUR FILESI am not responsible for any damage you might cause to your files, also if you already know this, cool, don't hate on me, there are people who don't know. Now, lets get started
Step 1: your first mod goes in its usual spot, the portal2 folder in your Portal 2 folder (theres a difference)
Step 2: Now this is where it gets odd, you have to create another folder labeled portal2_dlc3 and put another mod in there, and continue doing that only with different folders (replace dlc3 with dlc4 and above)
Step 3: Now load up Portal 2, you should get a loading screen-type thing, wait until the dots turn orange then kill it with task manager, now load up the game again and it should boot normally, now your mods are active, yay.