Select "Bus Operator" in order to drive the bus. Passengers only ride the busses, and Transit Police is a gamepass with a similar setup as the following steps.

You can use any bus on any route, and they all should fit each route roadway

You can use any bus on any route, and they all should fit each route roadway

Any route works, important that free-drive does not do any routes, and only adds the ability for the ODK4 Destination Sign Changer.

Press the "Skip Startup" button on the right of your indicator panel. After waiting a second for everything to start up, (Step 4) Press "]" or Up D-Pad on console to put the bus into drive. After, press M twice to open and close the door, in order for the door to properly seal.

Press P or B, and the parking brake indicator (Shown highlighted in red) should illuminate. This is important as in order to later start the engine, the parking brake is required.

Press C or L3, and the lighting bolt indicator (Shown highlighted in red) should illuminate. Press the control again and the electrics will turn into night mode, which is meant for runs during the night.

While having day/night electrics on, and Parking Brake on, (Should see yellow and red lit up on the indicator panel) Hold down the bus brake and press Z if you are on PC or Y if on console.

When you have your eleterics on, brake on, and engine running, press the "]" key or D-Pad Up control on a console in order to put the bus into drive. Once you have the bus into drive, release the parking brake by pressing P on PC or B on console and you should be able to accelerate and drive.

Press "0" (Zero) on your keyboard to view the first person view as an operator.

Press "T" on your keyboard to enable the mouse steering feature on all busses. This works in first person, along with 3rd person views.

Go Into the "INFO" menu on any bus and press the red box next to "Realistic Powertrain". This enables access to not only go faster, but brake faster, and operate the bus more realistically.
(You must use F to use this feature)

Press M to open front doors. You do not have to be in park for the front doors to operate.

When completely stopped and in park, press "N" to open the rear doors. 

When parked and at a complete stop, press "K" to kneel the bus. This release air pressure from the suspension, making the bus lower to pick up passengers that are at ground level.

To press exterior lights (Or just generally lights), press "L".
To press interior lights, press "J". Interior lights to not have an indicator on the panel.

To get a left signal, press "Q". To get a right signal, press "E". To get hazards (Both Left and Right signals at the same time), press X. You can see this in the red circled area on the indicator panel.

When opening it up, (By pressing "ODK4" on the left), press "DESTA" on the screen of the ODK4.

After opening the menu up, use the buttons on the right to put in a 3-4 digit code, that you can find on this sheet.  Use "Del" to delete the latest character, and "Clear" to wipe the code. Hit "Cancl" to not enter any code, and once you have your 3-4 digits entered in, use "Enter" to make the code appear on the bus / screen.

When opening it up, (By pressing "ODK4" on the left), press "P/R" on the screen of the ODK4.

After opening the menu up, use the buttons on the right to put in a 1-4 digit code, that you can find on this sheet.  Use "Del" to delete the latest character, and "Clear" to wipe the code. Hit "Cancl" to not enter any code, and once you have your 1-4 digits entered in, use "Enter" to make the code appear on the bus / screen. You can use a P/R code WITH a Dest A code at the same time.