Spread lentils onto a sheet of parchment paper and sort through them, discarding any debris you may find.
Transfer lentils to a fine mesh strainer, and rinse with tap water until water runs clear.
Stovetop cooking method:
Add lentils and hot water or broth to a large saucepan over high heat.
Bring to a boil, then immediately lower heat to medium. Cover the pan with a lid and simmer for 5-10 minutes. If using them in another dish, 5 minutes should be ideal. As a standalone side dish, cook them 7 minutes to 10 minutes for a softer, creamer lentil dish.
Season with salt and pepper or other seasonings of your choice.
Instant Pot cooking method:
Add lentils and hot water or broth to the inner pot. Cover IP with lid and close the vent to seal. Set manually to cook at high pressure for 3 minutes.
Once the pressure cooking is done, perform a quick release by carefully turning or pressing the pressure release on top of the pot.
Remove lid and season red lentils with salt and pepper or other seasonings of your choice.
Notes
Using hot liquid helps the Instant Pot to come to pressure more quickly, and also speeds up the time to bring a saucepan of water to a boil.
For firmer lentils, sauté them in a teaspoon of oil in the pot before cooking.