Take off the top of the filter. Inside should be full of oil. If the oil is clean it's OK, as it is used the trapped dirt falls to the bottom and slowly fills it up.
If the dirt has built up to the bottom register it is time to clean it out. Or you just want to clean it. Take the bottom part off by loosening the clamp. Then pour out the old oil and clean out the dirt with rags or cotton waste. Finally give it a wipe with a rag and some cleaning solvent (varsol).
The top part should be washed in varsol kerosene or cleaning solvent. Swish the solvent around but do not blow compressed air into it. Let it drip dry.
Put the bottom part back on the car and fill to the level line marked on the filter. Use 50 wt non detergent oil.
The factory actually recommended 50 wt oil so use that if you can find it. If not, the 30 wt will do.
They sell 30wt oil at Walmart as 4 stroke lawn mower oil.
If you did not take the bottom off or clean it, check the level and top up to the line.
Now you can put the top back on and you are done.
The factory recommended checking and servicing the filter every 1000 miles, or oftener if the car was used on dirt roads. Under extreme dirty conditions it could be necessary to clean the filter daily.
These days of paved roads your filter could go years between cleanings