A Power Unit is made of 6 parts. The Internal Combustion Engine (V6), Turbo, MGU-H (motor attached to the turbo), MGU-K (KERS motor), Energy Store (battery), and the Control Electronics (ECU and associated bits).
Each driver is limited to 5 of each of the above parts per season. They can mix and match individual components to build the Power Unit for each race.
If a driver uses more than 5 of any of the parts then that means they get a grid penalty (usually 10 places) the first time they use it.
They are also restricted on Gearboxes. Each gearbox must be used for 6 consecutive races. If a driver takes a new gearbox before it has done 6 races, they get a 5 place grid penalty.
Each driver is limited to 5 of each of the above parts per season. They can mix and match individual components to build the Power Unit for each race.
If a driver uses more than 5 of any of the parts then that means they get a grid penalty (usually 10 places) the first time they use it.
They are also restricted on Gearboxes. Each gearbox must be used for 6 consecutive races. If a driver takes a new gearbox before it has done 6 races, they get a 5 place grid penalty.