Please help me with these:

1. Difference between 'to' and 'for' and give some example sentences
For me, TO is used with a verb, like the infinitive and FOR is used with a noun or gerund.
2. Why cant we say angry to?
For me, angry is only used with AT or WITH and not TO but I can't explain the difference between angry AT or ANGRY with.
3. could have Vpp means regret only?
For me, it's a yes. For example, It could have been a lot easier to ride the bus.
4. The difference between instead of and instead
For number 4, I really don't know the difference.

I hope you guys can correct me. Thank you so much!

Be sure to use a good dictionary to help you with words' actual meanings and parts of speech. Here's a good one: http://www.merriam-webster.com/

Read about "to" and you'll find it does far more than simply be the word indicating a verb's infinitive form:
http://www.merriam-webster.com/dictionary/to
Do the same thing with "for."

The usual idiomatic phrasing is "angry with" or "angry at" -- and they mean approximately the same thing. I tend to use "angry with" when it's followed by the name or a reference to a person, but I don't know if that's common or not.

Sometimes having a list (or a link) of phrasal verbs is a handy thing to have around, too. None of these can be explained, though; they simply are normal and common expressions.
http://www.englishclub.com/vocabulary/phrasal-verbs-list.htm

The verbs "could," "would," and "should" are past tense forms (in your sentence, present perfect which is one of the past tenses) and usually are referring to possibilities, not factual occurrences.

instead -- http://www.merriam-webster.com/dictionary/instead

instead of -- http://www.merriam-webster.com/dictionary/instead%20of

Let me know if something here doesn't make sense.

Thank you so much! Very big help indeed!

You're welcome!

1. You have a good understanding of the basic difference between 'to' and 'for'. Generally, 'to' is used to indicate direction, destination, or purpose. It is often used with verbs or infinitives. For example:

- I am going to the store.
- She wants to go to the beach.
- He gave a present to his friend.

On the other hand, 'for' is used to indicate purpose, benefit, duration, or recipient. It is often used with nouns or gerunds. Here are a few examples:

- This gift is for you.
- I bought some flowers for my mom.
- I am learning English for my career.

2. You are correct that we usually use "angry" with "at" or "with". The difference between "angry at" and "angry with" lies in the level of personal involvement. When we are angry at someone, we usually feel stronger negative emotions and blame them for something. When we are angry with someone, the negative emotions are present, but there might be a lesser sense of blame. For example:

- I am angry at my brother for breaking my phone.
- She is angry with her friend for forgetting her birthday.

3. While "could have + past participle" can be used to express regret or missed opportunities, it is not the only meaning or usage. It can also be used to talk about hypothetical situations or possibilities. Here's an example:

- If you had come earlier, we could have finished the project sooner.

In this case, it doesn't necessarily indicate regret but rather an unrealized potential outcome.

4. The difference between "instead of" and "instead" lies in their respective usage.

- "Instead of" is used to show substitution or choice between two options. For example:
- I'll have tea instead of coffee.
- She played tennis instead of going to the party.

- "Instead" is used to indicate a replacement or a preference for one thing over another. It often means "in place of" or "as an alternative". For example:
- I'll go for a walk instead.
- We decided to read instead of watching TV.

I hope this clears things up for you!