To cover something completely with water or another liquid.
Submerse can make people think of swimming, diving, or being underwater.
Examples:
I submerse the toy in the bathtub.
The rain will submerse the garden.
Don't submerse your phone in the pool!
If you submerse your sandwich in the soup, it will get wet.
The huge wave will submerse the whole beach.
She submersed herself in the lake and swam for a long time.