Reddit is a really mixed bag of all sorts of stuff. It is divided in to “sub-reddits” which are curated by volunteers of all sorts and shapes. Each sub-reddit has it’s own flavour depending on who the moderators are and how zealously they guard their domain or how friendly they are. reddit/r/drawme is one of the friendlier areas of reddit.
People ask for drawings of photos. Other people have a go at drawing the photos and post their work as replies. The rules ask that you don’t delete posts. This is helpful as someone could have spent hours drawing your photo only to find no place to reply. It’s also good publicity for the artists for other people browsing their work.
There is no obligation to pay the artists, however it is a helpful gesture. The chance of being paid helps attract better work. Many drawings are done on the computer, but some are physical drawings on paper or canvas. Some artists will be happy to post the work to you. If in doubt - ask!
Happy browsing: http://reddit.com/r/drawme