Whether you can swim with your watch depends on the stated water resistance and the relevant ATM class.
Please always check the details for your model. Not every watch is suitable for swimming. Everyday splashes are different from prolonged contact with water or movement in water.
Make sure the crown is fully closed before the watch comes into contact with water. For screw-down crowns, the crown must be correctly screwed in.
After contact with salt water or chlorinated water, you should carefully rinse suitable models with clear water and then dry them thoroughly.