My friend has a 1968 dodge 3/4 single cab 2wd pickup. He was wondering if there was anyway to make it as good as a 4wd. Thanks

How so?
Eat more gas, roll over easier, higher insurance, bigger more expensive tires, more parts to break, what?

he just ues it for a playtruck. He wants it to perform better in the mud.

You can install a lift kit, larger off road tires and a traction device such as lockers or limited slip.

You may think im stupid but whats a locker?

Lockers are installed in the differential to lock both axles together.
That way you can't just spin one tire and get stuck easy.
You can engage and dis-engage them at will. You would only lock the axles for off road use.
Limited slip is on all the time and is a on/off road compromise.
My Jeep has a limited slip rear differential.

Where can you find lockers, and are they hard to install?

You will need to go to a shop that specializes in 4x4's.
They can set you up, be ready to spend a $1000.