Cars are grouped by team (LSM/LMM, B1 Engineer/Technician, B2 Engineer, Cat A Technician, Cabin Team). Tap "Loan this car" on any available (green) car, enter your staff number, and your name fills in automatically if you're already in the system. If not, you'll be asked to register your name on the spot. Complete the short vehicle inspection checklist (exterior, interior, fuel level - defaults to "Yes" so it's quick, just flip anything that's not OK to "No") and confirm the loan.
Find the car (shown in red / "Loaned Out"), tap "Return this car", and confirm the staff number of whoever is returning it - it doesn't have to be the same person who took it out.
Noticed something wrong with a car (dirty, AC not cooling, dead battery, etc.)? Tap "+ Add a remark" on that car's card. It shows as a warning banner on the card for everyone until someone clears it (up to 5 remarks can be open on one car at a time). No login is needed to add or clear a remark.
The bar under the header shows which of the 4 rotating teams (A/B/C/D) is currently on duty and whether it's the Day (06:00-18:00) or Night (18:00-06:00) shift - this is calculated automatically and gets attached to every loan record, no manual entry needed.