To load up something (or load something up) is to put a lot of things, or something heavy, into a vehicle or machine.
Examples of use:
1. Can you load up the washing machine and switch it on while I’m at work, please?
2. The workmen loaded up the truck.
3. I’ll just load up the car with our luggage and then we’ll set off.
infinitive – load up
present simple – load up and loads up
-ing form – loading up
past simple – loaded up
past participle – loaded up