What is the difference between zusehen and zuschauen and And what is the difference between " zusehen" and "sehen"? ?Feel free to just provide example sentences.

Zusehen and zuschauen are synonyms, although "zuschauen" can be used to mean "hurry in your pursuit". As an example "Du solltest zusehen die Miete zu zahlen" means "You should watch yourself paying the rent" with the implication being a threat of "or else...".

The difference between zusehen and sehen is is that zusehen would mean "to watch someone/something else", as in, watching your friends play a game, while seeing is a general see/seeing/watching. Not all contexts use it clear-cut, unfortunately. You'd generally use "sehen" when talking about a movie, for example. "Ich sehe einen Film" = "I'm watching a movie". But if you were to ask someone else to pay attention instead of playing on their phone you would say "Kannst du bitte zusehen?" = "Could you please watch?"

Edit: Actually, I believe even in the threatening context I explained, you can also use either zusehen or zuschauen, it's more of a regional thing, perhaps? I forgot that, but yes, they're essentially always synoyms.