Here is some help for the Ikarus series made by Bustrainz.
The level of realism is high enough that you almost need driving licence for truck at least to figure things out.

Get started:
- Jump into the driving seat
- Switch on the batteries - press E, or tap the right arrow button til you see the dashboard. Make the steering wheel disappear and click a black switch in the middle - and the dashboard is "alive" now.
- Press the red button near the key to start the engine. Depending on how you set the maintenance level and weather conditions, you need to apply throttle by Num8 to make the Rába engine jump in. Quick tip: you can shorten it by pre-heating the engine. In the passenger compartment open the first lid on the floor. There is a valve for heating. Click on it. Go back to the driver's seat. There is a panel near the left leg of the driver. The upper one controls the pre-heater and the circulating pump. Switch to the upper position to ignite the heater and have the pump on. Wait until the coolant temperature reach 40 Celsius and start. The engine jumps in immediatelly.
- Very tedious part, wait til the compressor fills up the pneumatic system. It takes a couple minutes, because the two brake circuits, the auxilary circuit for the doors, and the circuit for the air springs need to be filled. Wait til the big red indicator is off or the bus lifted up from the "kneeling".

Driving:
The bus has a manual transmission, 6 speeds.
- Start from second gear, the first gear is needed at hill start only
- Shift up at 1800-2000 rpm at flat ground, when you go uphill, 2100 rpm.
- Cruising speed is at 1500-1600 rpm, so the Citybus series has 50km/h at that rpm, the Regiobus has 60km/h.
- The motor brake works by the "K" key in default. It has a very distincive sound - the hungarian slang for it is "bubu".

How to shut the engine down:
- Switch to neutral, and press the "K" key. It shuts the engine down.
- When the air pressure is not sufficient enough, you have to stall the engine. Press the Tab key + any number key from 1 to 6, the release the Tab key.

Heating:
- Open the valve under the first lid on the floor
- Near the driver's left leg there are two panels. The upper one controls the "Thermal" heating. Flip the switch to the upper position for
pre-heat the engine and turn the circulating pump on. When the engine is warm - 80 degrees Celsius - flip the switch down for the
circulating pump only.
- The seond panel controls the dry-air heater. The closer switch to you controls the heater, up position is heater, middle is off, down is
ventilation. The further one controls the intensity.