To check the oil level, open the hood of your car and locate the oil dipstick. Remove it from the engine and wipe it clean with a towel. Then reinsert it into the engine until it is seated. When you pull it out again, the oil level should be within the two marks on the dipstick.
If the oil level is low, add enough oil to bring it up to the full mark. You should then check the oil level again after driving your car for a few minutes. If the level has dropped significantly, you may need to have the oil pump checked.
If the oil level is full, you should take your car to a mechanic to have the oil pressure sensor checked. This is not a serious problem, but it can be a sign of a more serious problem.
In the meantime, you should not drive your car any more than necessary. Driving with low oil pressure can damage the engine and lead to costly repairs.