I looked at snapchat once. I really don’t understand it. What purpose does it serve? Am I too old to understand it?
snapchat was originally for sexting, but now it's basically the "photo" version of facebook. You make updates (stories) constantly, which always refresh. You can either send each other photos or texts, which auto-delete. Now corporate shill companies are using it to "spread news" and C-List "hawt" celebrities like Kylie Jenner and DJ Khalid use it to promote their brand.
You can also use AR filters on your face, draw stuff or add cartoon pictures of yourself (Snapchat bought Bitstrips)
If a girl doesn't want to give a guy their number first, they give them their snapchat.
I use it regularly though. I don't use instagram often, facebook mostly for pce groups and access to other sites, and I stay far, far away from Twitter.