I have a 55 Chevy 210 and I want to clean the metal air filter. How do I do that?

Vacuum around the furnace with a wet/dry vacuum or the hose attachment on your upright vacuum. Take out the air cleaner from the furnace and sweep up as much dust and debris as you can. If you vacuum before wetting the filter, the dust and dirt can turn to mud and be difficult to clean. Spray the air filter with water. For this, a kitchen sprayer works well; if the weather is wet, a garden hose may be used to remove any residual particles. Wash both sides of the filter with a mild detergent such as dish soap. Rinse the dish thoroughly. Dry the filter as thoroughly as possible with a dry cloth or paper towel. Then air-dry the filter until it's fully dry.