https://support.chess.com/customer/en/portal/articles/1444880-what-do-i-need-to-know-to-get-started-with-online-chess-
You can be randomly paired if someone that meets your seek settings also has a seek out the same time you do. Or players can manually select your challenge from the Open Challenges list.
You can also directly challenge other members, if they are open to challenges.
yes you are randomly assigned an opponent but the rating depends on your settings ie i set mine to -100 to +200 and for example if you play 24hr you have 1 day to make your move or 24hrs 
Interesting. One whole day just to make a single move!
You can make one move the time allotted, from one day up to ten days depending on the time controls; however, if both players are active and visit the site daily several times per day several moves can be made and possibly even the whole game can be finished in one day depending on if both players are moving. You can join matches with clubs you belong in against other clubs or you can join daily tournaments.
What is "Daily Chess"? How does it work? I mean, are you randomly assigned an opponent or one is chosen that has a similar rating?
I'm clueless.