It's pretty tricky. Each set of synonyms carries a different connotation that is hard for a non native speaker to understand. I think the best way is to practice you English, ie speaking or watching a movie, and see how native speakers would use it. For example, with the sentences you wrote, freaked out and shocked sound very similar in definition, but as a native speaker, I see them as two completely different things. If you are shocked, that means that you are very surprised. If you are freaked out that means that you are surprised but also scared. If you see a massive spider, it may freak you out. If you are not afraid of the spider, you may still be shocked that the spider so big. It doesn't scare you, you've just never seen such a big spider. Hope that helps :)

You have to know the emotive sense - the feeling. But also, the register. So, 'freaked out' is very colloquial and informal. And yes, I agree it has a different meaning to shocked. Try and get teachers to talk about registers of different words, and the emotive sense as well. The only way, apart foorm those mentioned above, is to ask, and ask, and ask.

It helps so much. Thank you!

Hope that helps!

I guess every synonym has a slightly different meaning and that is how you choose which one best applies to the emotion you want to describe. For example, "shocked" is more to describe the brief burst of energy (or "shock") you have when you are surprised, whereas "freaked out" implies a sense of fear or a bit grossed out, so you might more it when you are surprised but with a fearful/disgusted type rather than a happy surprise.