Combine the lentils and water in the bottom of the Instant Pot. You can add up to 1/2 teaspoon of salt if you want them seasoned, but keep in mind that they may turn out a little more firm that way. Don't season with salt until the end of the cooking cycle if you want to guarantee soft lentils.
Secure the lid and move the steam release valve to Sealing. Press the Manual or Pressure Cook button to cook at high pressure for 9 minutes. (They will still have a little bite to them this way; cook for 10 minutes for softer lentils.) It will take 10 minutes for the pot to come to pressure before the cooking cycle begins, so the screen will just read "On" until then.
When the cooking cycle completes, immediately move the steam release valve to Venting to release the pressure right away. Make sure your hand isn't over the steam release valve, to avoid the hot steam touching your skin. When the floating valve in the lid drops, the pressure is released and it's safe to open the lid. (If you forget to release the pressure right away, it will still be okay-- your lentils will just be softer when you remember to go check on them.)
Stir the lentils and make sure they are tender to your liking. You can always add an extra 1/2 cup of water and pressure cook them again for 2-3 minutes, if you want them softer, but they should be done at this point. There shouldn't be too much liquid left in the pot, so you can use them right away without draining them.
Use a slotted spoon to scoop them out, then serve warm. For serving ideas, be sure to check out the post above! You can store cooked lentils in an airtight container in the fridge for up to 1 week.
Red lentils cook in just 5 minutes at high pressure with a quick release. Keep in mind that red lentils will have a mushy texture no matter what, so you can cook them longer if making a soup or curry with them. They will completely dissolve into a soup and will act as a thickener if you cook them for 10 minutes at high pressure, like in my Curry Chicken Soup recipe.