Hi, The expression, 'Just do it' (like in the Nike ads) is used more than 'Just act' Some people are always thinking about what they should do, need to do or are going to do. They spend so much time thinking or talking about what they are going to do but they never actually do it. We say they 'procrastinate' which means they waste time and don't do what they should do. Sometimes if you think about something too much it makes it harder to make a decision to start doing something. For example, some people are always saying they need to study more to learn a language. They talk about what they should do but never actually spend time studying. As a result they don't improve. When I think about the people I know, I admire people who are always trying new things and are not scared to step outside their comfort zone (do something you feel nervous about becuase you haven't done it before). I think if your attitude to life is 'Just do it' you will achieve more and have more fun in life.

Your question should read "What does the phrase "just act" mean?" Does it mean for example, "Don't think too much. Just act?". Yes you are right, other ways of saying this would be, 'Just do it or don't delay!'

It simply means "do it"

You will see "Act now!" often in advertising. It means "Buy now! Order our product now!" This is typical with the style of advertising called "infomercial". Usually, the product is some sort of "gadget" for exercise, for the kitchen, for cleaning, for leisure, etc. These commercials are usually on television late at night or early in the morning. They often will say things like this: "Act now, and we'll give you another whole set ... for FREE!" "Act now, and we'll throw in (add) this amazing [extra product]!" "Act now, and we'll cut the price in half!"