As a SnapChat user, I don't really notice "ads." There are things like stories (which I am guessing are things that they charge money to people to get placement) and promoted filters and overlays you can put on your pictures. But when I am watching a friend's SnapChats, I am never interrupted by advertisements.

I really wonder what is the amount of revenue that they are generating through advertising. Off the top of my head, my recollection is that 95% of the time I open snapchat I do not really see an advertisement. I don't use the discover section, I almost never look at the "stories" and friends very rarely use promoted filters. I wonder how effective ad buyers are finding the SnapChat advertising platform. This is pretty highly contrasted to my recall of Facebook which I see advertisements nearly 100% of the times I open the app. I am a regular user of both apps.

Snapchat is often used for sexting, but certainly not mainly.

Think Twitter for pictures, as a vague comparison. Quickly consumable and disposable updates in picture form. Compare to Instagram, which has a somewhat higher quality expectation because the posts are permanent. There's also an expectation that people will post less frequently, while with Snapchat, it's not unheard of to post a dozen updates in a stretch.

They have ads.

Not used just for sexting.

>I thought they were mainly used for sexting am I wrong?

Completely. Mainly used for sharing random photos of your day. Food, sights, etc.