Ah with g-mod 13, it's a little different. You have to go to View All or something like that... it doesn't quite support the classic Addon system, I don't know what direction Garry is taking it in. So it's a little extra hurdle at the moment.
Thank you for reminding me about Garrys Mod and having this thread for someone to link the adult website the likes of which I could not find after hours of googling. Are there more websites like that? That one seems a little small.
Anyway, I thought I would contribute something I just spent a little while figuring out:
I believe they changed the system so that when you load up a mod and want to put it in the game, you hold Q and then you have to look for a tab at the top that says "Browse." If the mod maker made their mod correctly, apparently in the new format, then you will see their name like "vaako's characters" which is the name of the file folder in the addons directory.
I downloaded some other models at garrysmod.org and they were not in the same format. Their zip file just had two folders for models and materials. If I'm not mistaken, it used to be that you just drop those two folders into the addons directory and they would be in your Q menu right away, or they would replace alyx or something I don't remember, I used gmod years ago before today. Anyway, just dropping those folders into 'addons' did not work today, so I did something else and it worked:
I made a new folder in the addons directory and called it "cammy" (hehe..) and put the models and materials folder in there. It did not show up until I copy and pasted this text file from vaako's folder called info.txt and I opened it up and changed references to vaako to just say cammy instead. I guess in some menu that cammy text will show up, and maybe i did not need to change it, but sure enough the program is looking for that text file and after I did that it worked. I also downloaded a different model with a folder in their zip file called settings. I went ahead and ignored that settings folder and just copied models and materials and the text file, I didn't even try so who knows what that settings folder does.
Hopefully this helps someone! Or maybe I did something simple wrong and this was all unnecessary!
Please help me find more garrys mod vixens! I think I browsed the entire garrysmod.org and digital ero and I've got like ten models... liara, miranda, cammy... I feel like there should be more... if only I could find a draenei...