1) "Take it up a notch" means to increase the intensity or quality of something. A few examples:
- If you're playing in a band and a bandmate says "let's take it up a notch", that means they want to play faster, louder, or more energetically somehow.
- If you're cooking food with someone, and they say "let's take it up a notch", that means they want to make it more spicy or more flavorful.
The meaning is a visual reference to some sort of switch or knob with multiple settings. They often have marks or "notches" to indicate levels, like volume level or temperature. "Let's take it up a notch" implies that you want to turn the metaphorical (or actual) knob to a higher setting.
2) "Happy-go-lucky" means someone or something is very cheerful and unconcerned about negative things. A happy-go-lucky person is always happy and doesn't worry. A happy-go-lucky book/film or something similar has a very light-hearted theme and doesn't discuss serious topics.
3) This is generally phrased as "putting two and two together". This means that someone has discovered the answer to some puzzle or complex situation and fully understands now. It can also have the meaning that something has been hidden from that person; "putting two and two together" means they figured out that they've been misled or discovered clues and now know the secret that was hidden to them. An example:
- "No one has told John that he will lose his job, but I think he's put two and two together." This implies that John has seen other clues to indicate that he will lose his job, and he is now pretty sure that it will happen even though no one has explicitly told him.