• The total amount of money you have, in euros
• Indicates how tired you are. If it is nearly filled with blue, you will need to get some rest as soon as you can, otherwise you will experience unpleasant black-out / dozing effects, not to mention falling foul of the traffic offence of driving too long without a rest. This feature only applies if you enable fatigue simulation in the gameplay options.
• The condition of your truck. The more red you see, the more your truck is damaged. Note that the damage will influence the truck's performance!
• The condition of the cargo. The more red you see, the worse the damage to the cargo is. Be careful, some cargo is more fragile than others. If no trailer is attached, this field is left empty.
• The current game time (different from the real world time or your system time).

More about ETS game rules you can read in Euro Truck Simulator Manual.