A depth chart ranks players per position and sorts them on their playing time probability. Starters are ranked highest, because they are perceived to be the best at the position by their coach.
Depth charts are made by position or detailed position. In football you could make a depth chart with goalkeepers, defenders, midfielders and forwards. Or you could make one for each position in the team’s usual formation. Eg. in a 4-3-3 you’ll have a starter left back and a 2nd or even 3rd string backup.
As a fantasy sports player you would want to pick starters or 2nd string replacements, as they have the highest chance of playing and therefore score more points.