You can equip your train with staff to improve the performance of your train. Every train can have up to four staff-persons: a train engineer, a fireman, a train attendant and a security guard. Select one of your trains and press
to show the details of this train. Right in the middle of the screen you can see the four slots for the staff (one slot for each possible job). Select a free slot and you will see a list of persons you can hire or use for this position. Select the person you want to hire by pressing
. If you do this with all four slots you have a fully staffed train and will get the achievement immediately.
Note: If there are currently no persons you can hire for one of the slots you have to wait some time until new persons apply for this job (you will get a notification on the top left corner of your screen when someone new applies).