Snake drafts are the default draft type on Sleeperbot, and are commonly used because they allow for a fair and balanced draft. In a snake draft, each fantasy coach has one pick in each round. Each team makes its first-round pick based on a predetermined order. When the first round is over, the team that picked last in the first round picks first in the second round — in other words, the draft snakes back on itself. The team that had the first pick in the first round now has the last pick in the second round and the first pick in the third round.
Keeper simply means you select a certain amount of players to keep going into the next year. For example, let's say your league decides to have two keepers every year. You'll keep the two best players from your roster in 2015, and then the league re-drafts the rest of the players who are not kept. Keeper rules can vary quite a bit across leagues. It is up to the commissioner and league members to decide what keeper rules they would like to institute. To set keepers, just ask your commissioner to enter the keepers onto the draftboard before your draft begins. Your commissioner has full edit control over the draftboard, and can set players in advance by double clicking into any square on the draftboard and choosing players to keep in advance.
Dynasty owners can keep an entire roster for the next season. These leagues keep most or all of the players on a team, and force owners to think about the future. If you're starting a dynasty league, the first draft will need to focus on setting yourself up for long-term success. Sleeperbot will offer the ability to roll your rosters over at the end of the season to start a dynasty league. Your league data will be stored so that you can easily restart the league with your friends at the start of next season.
(coming next year)
In Auction leagues, instead of having a snake order of picks, owners start with a set amount of money to bid on players. Any owner can bid at any time, as long as they have money left. You have to choose wisely, though. If you blow all your money on Antonio Brown and Todd Gurley, your remaining funds won't help you fill out your roster well. We do not currently support auction drafts, but plan on adding this functionality next season.
If you prefer to do a non-standard / non-snake draft you may be able to do that as well, but it will require a small manual work-around by the commissioner. For example, if you want to manually edit the draftboard to bend to your league's particular rules, you can do so by asking your commissioner to manually enter each pick into the desired square. The draftboard is fully editable by the commissioner.