Rinse the lentils in a sieve under cold, running water.
Add lentils and 3 cups (700 ml) water to a medium-sized saucepan. Bring to boil; reduce heat to a simmer and simmer, mostly covered, for 5 minutes. (You may need to tip the lid a little to the side, to keep the pot from boiling over.)
When the lentils are soft, drain off excess water and use as desired.
Instant Pot Method
Add lentils and 2 cups (474 ml) water to bowl of Instant Pot.
Cook on high pressure for 5 minutes. Allow for natural release of pressure for 5 more minutes.
Then, carefully tap the valve to release any remaining pressure before opening the lid.
Don't add salt to the lentils until after cooking, or they can become tough.
You may want to forgo seasoning altogether until you incorporate your cooked lentils into another dish.