If using spaghetti noodles, break them into thirds and add them to the pot in a criss-cross manner, to help prevent them from sticking together as they cook. For other types of short-cut pasta, you can just pour the noodles into the pot. Add in 5 1/2 cups of water and add a teaspoon of salt. It's okay to give the pasta a stir if you're using the short-cut pasta, but do not stir spaghetti noodles. (Spaghetti noodles might stick out a bit from the water, but that's okay because they will sink in as they soften and cook.)
Secure the lid and move the steam release valve to Sealing. Use the Manual or Pressure Cook button to cook at high pressure for 3 minutes. It will take roughly 15 minutes for the pot to come to pressure, so the Instant Pot will only read "On" until the floating valve in the lid pops up, signaling that the pot is pressurized.
When the cooking cycle is complete, let the pressure naturaly release for 10 minutes. When the screen reads LO:10, you can move the steam release valve to Venting to release the remaining pressure. (You'll know it's safe to open the lid when the floating valve in the lid drops.)
Give the pasta a stir and check to make sure it's tender enough, then drain and rinse the pasta to remove any excess starch. Serve warm with your favorite pasta sauce and toppings.
Follow the directions above for either spaghetti noodles or short cut pasta, but use a cook time of 0 minutes (yes, zero minutes) instead of the 3 minute cooking cycle. When the cooking cycle is complete, allow the pressure to naturally release for 8 minutes. When the screen reads LO:08 move the steam release valve to Venting to release the remaining pressure.