Decisions allows for several different types of advanced voting methods.
The most common voting method is Simple Plurality, where each voter gets to make one choice, and the candidate with the most votes wins.
Approval Voting is a system where voters can give a yes or no vote for each candidate on the ballot. The winner is the candidate with the most approval votes. So if you like 2 out of 3 candidates, then you vote for 2 out of 3 candidates.
Ranked Choice - Instant-Runoff
In Ranked Choice Voting, voters can select candidates in order, by ranking their choices as first, second, third, etc. One type of Ranked Choice Voting is Instant-Runoff. The idea is that when votes are being counted, you gradually drop out the candidates with the least votes until there is one candidate with a majority of votes. If your first candidate is dropped out because of too few votes, then your ballot goes to your second choice. You can vote for multiple candidates in the order you prefer.
Ranked Choice - Borda Count
Another type of Ranked Choice Voting is Borda Count, where a certain number of points are awarded to the candidates based on voters' ranking preferences.
Ranked Choice - Condorcet
You can also do Condorcet style Ranked Choice Voting. The main point here is that the winner is determined by seeing which candidate performs best in heads-up matchups against the other candidates.