Chicken Basics
Chicken breasts will be the most expensive at the store, and they will need the most prep. They come in large packs, but are usually easy to find in a 2 pack. They have quite a bit of "added water" so they'll need more draining as you cook so they brown up, and don't inadvertently taste boiled (which is not yummy).
Now you can continue cooking the chicken, flipping it around every few minutes until both sides are golden brown. You know it's done when you can easily break a piece in half with your spatula and it's white all the way through.
Thin sliced chicken breasts will be less expensive and will need less prep. They'll come in larger packs, but because they're thinly sliced, a pack will usually give you the equivalent of 3 full sized breasts worth of meat.
Tenders are the least expensive and just require that you cut out the veiny part at the top. They cook the fastest and have the least "added water" so they brown up nicely.
Whichever you choose, dice it up into small pieces. I prefer to cut it on paper plates so I'm less worried about salmonella on a cutting board. Always clorox wipe your counter afterwards, wash those utensils in hot soapy water, and take out the trash before bed. Leaving the empty chicken container and pieces you've trimmed off will smell awful by morning.
Cooking:
Add 2-3tbsp vegetable oil to a medium sized pan and turn the heat to just above medium. Wait 1min for the oil to warm up and then add your diced chicken. It will sizzle and splatter almost immediately. Spread the chicken out like a blanket in the pan and leave it.
It will slowly turn white on the bottom. Don't flip it yet. You want to the white to be just more than half way up the chicken pieces, and then you'll flip it with a spatula.
Once flipped, you'll notice that the pan seems to have water in it now. That's the "added water" cooking out of the chicken. You want to remove that so your chicken doesn't taste boiled or steamed. Place a folded-up paper towel in the pan and soak up the greasy water. It will be very hot so don't take it out with your fingers. Instead, use the spatula.
The chicken is now ready for whatever seasoning you plan to use. Once cooled you can store this chicken for 3-4 days in the fridge with or without seasoning. You can also divide it up and add different seasonings so you have some for salads, pastas, bowls etc.