How do you wire a 3 wire cord to a 4 wire plug?

You cannot wire a 4 wire dryer plug into a 3 wire outlet for mobile home use - (US NEC) - you must carry all four conductors all the way back to the distribution panel. In a hard wired house...

Use a UL approved grounding adapter for this, it has either a fork terminal that goes over the wall plate's screw, or an actual pigtail that must be attached to a good ground.

Black wire to brass colored terminal. White wire to silver colored terminal and bare wire to green terminal.

Can you combine the black and red wire and connect it to the black wire from the house and have standard 110V service? Just take a little longer to cook?

Change the cord of the device to match the receptacle. This would assume no need for a neutral. Read your manual for power requirements.