You can allow your employees to choose their own schedule by posting available shifts, which they can then apply to. You also have the option of allowing those shift applications to be automatically approved, so shifts are assigned on a first-come, first-served basis.
Go to Dashboard > Settings > Company Settings, then scroll down to Available shifts and shift offers. Switch the toggle to "Yes" for Automatically approve applicants, and as soon as an employee applies for a shift, it will be theirs.
If you would like to review applicants for each shift, simply leave the above setting on "No" and you will be able to choose which employee gets each shift.