Vehicles must have a disc on them showing that they have paid road
tax to the government, which lets the owner use the road.
Drivers must be insured before they are allowed to use the roads.
This is very important, and you could be heavily punished for not paying.
If a driver does not have tax and insurance they are breaking the law, and they are likely to be heavily punished if the police catch them.
It's also not allowed to let someone who isn't insured to drive your car, even if you are in it with them.