From your leads dashboard, click Settings > scroll to the bottom.

From Round-robin staff assignment, enable and add your participating staff.

After submitting, all new leads will be automatically assigned. Note this will not assign leads to staff that came in previously.

Below, a new lead has arrived named John Johnson. If we click on it, we'll see its already been assigned to a staff member.

To the left we can see its already assigned to Dave. To the right we can see that some sequences we have set up for our leads have already sent messaging to John, and that a staff task to place a Welcome Call to John has been assigned to Dave.