Act: "act" can be a noun and it can be a verb. Example: "You act ridiculous when you are drunk" - In this example "act" is being used as a verb. Example: "He put on this act, trying to impress a girl"' - In this example "act" is a noun. This is sort of a colloquial term, meaning that he was trying to impress a girl. More Info: Action - to run is an action, to write is an action, to swim is an action. OR running is an action, writing is an action, swimming is an action. More Info: Action - "Action!" it can be a demand to act, or to take action. Meaning that you want someone to do something. Hopefully this is somewhat useful, if it isn't, let me know and I will expand more!

Act as a noun usually refers to something theatrical. In a play, for example, Act I scene II. Action is more general.