Rotation
From NSB User Guide
Pitching Rotation
Adding and Moving Pitchers
To add a pitcher to the rotation, find him in the list of Eligible Starters, click on his line, and drag him leftward dropping him into the slot of your choice.
To move a pitcher within the rotation, drag him up/down in the Starting Rotation.
[Video - Adding pitchers to the rotation and moving pitchers within the rotation.]