1. Park the vehicle on level ground and wait a few minutes with the engine off to allow the oil to drain back into the oil pan.
2. Open the hood and find the dipstick. 
3. Pull out the dipstick and wipe it clean with a clean cloth or paper towel.
4. Reinsert the dipstick, making sure it is fully inserted.
5. Pull out the dipstick again and observe the oil level.
6. The oil level should be between the “MIN” and “MAX” marks on the dipstick. 12.
7. If the oil level is below the “MIN” mark, you need to add oil.

1. The “MIN” mark indicates the minimum limit of the oil level. If it is lower than this mark, you need to add oil.
2. The “MAX” mark indicates the maximum limit of the oil level. If it is higher than this mark, you need to drain some oil.

Foam on the dipstick may be due to the following reasons:

1. Water has entered the engine.
2. Other liquids, such as gasoline or coolant, have been mixed into the engine oil.
3. The engine has been running at high speed for a long time.

If you find foam on the dipstick, it is recommended to go to a professional auto repair shop for inspection as soon as possible.

The dipstick generally does not need to be changed regularly, but it may need to be changed if:

1. The dipstick is damaged or deformed.
2. The scale on the dipstick is unclear.
3. The dipstick cannot accurately measure the oil level.

It is recommended to check the oil level at least once every 1,000 km or once a month. If you frequently drive long distances or in high temperature conditions, you should check more frequently.