I'm having trouble getting my keyboard to do what I want it to do.

this is at the top of my class

        KeyboardState currentKey;
        KeyboardState previousKey;

and this is in my update

currentKey = Keyboard.GetState();

            if (checkKey(Keys.Left))
            {
                ship.shipPos.X -= 4;
            }

            if (checkKey(Keys.Right))
            {
                ship.shipPos.X += 4;
            }

            if (checkKey(Keys.Space))
            {
                addBullet(bulletFirePos);
            }

            previousKey = currentKey;

this is the checkKey class

        public bool checkKey(Keys key)
        {
            return (currentKey.IsKeyDown(key) && previousKey.IsKeyUp(key));
        }

The bullets are shooting fine, one bullet every press of the spacebar...although when I shoot the first bullet it stays right in front of the ship and doesn't move...but thats not a keyboard issue lol. The problem I'm having is with moving left and right. I have to repeatedly press the key to get the ship to move and that's not what I want. How do I change the method so that if I just hold the key down the ship moves?

As Andy said above, IsKeyDown is what you actually want in that scenario.

If your bullets aren't moving, you're probably not updating their position every frame :)

the keyboard solution gave me worked. But it's just the very first bullet being created lol. As soon as I start the game and press space, it stays on the screen and doesnt move, but each bullet after that works fine!!