Auto-start is when a tournament begins automatically as soon as the a predetermined number of players have registered.
If you want to avoid playing low rated players in a tournament, that is easy. Just register for a tournament designed for players with a rating range that you like. Chess.com has lots of tournaments, so you can register for their next tournament in the 1601 to 1800 range.
If you want to avoid low rated players when you start games, just "create a new game," with a "random opponent," and then "click for more filters." Then you can specify the rating range that you would like to play against.
I hope that helps.
Please what is an autostart? I want to avoid playing very low rated players, eg in the 1000 or so. How do I generally do this.