The Type Keystroke action lets you type a single keystroke, pretty much any kind of keystroke you can type on the keyboard.
The Type Keystroke action is just like typing yourself, so you can type any keystroke and any number of them, but it can be tedious to create a sequence of keystrokes in a macro.
Use Type Keystroke when:
You can optionally have the key pressed and held, or pressed and repeated, or released if you previously pressed it.
Note: keys that are pressed stay pressed only as long as the macro continues to run.
You can also optionally choose (v8+) which application to send the keystrokes to. This allows you to send keystrokes to an application in the background. Note that the system and many applications do not expect to see keystrokes in the background, so how well this solves any given problem will vary depending on the exact circumstances.