How to know if a comma is needed before "what"

The comma is needed

1. When "what" is a union or union word and parts of a complex sentence. For example: That evening Igor realized that he had lost the meaning of life.

2. In some cases, when "what" is part of a compound union. “Because”, “because”, “because of that”, “because of that” and others. They are more often included in the subordinate clause in full, that is, a punctuation mark is placed in front of the entire compound union, but there are also cases when parts are separated. A comma is needed if:

The main sentence should be distinguished logically. For example: This is because you've been messing around all day.
There is a particle "not" before the union. For example: I refused to go to the store, not because I had no time.
Before the union there is an introductory word, adverb or particle. For example: Gregory was polite only because he did not want to quarrel.

3. In combination "only and … what" in two cases. A comma is needed here if:

After “only” is the verb “to do” or “to know”, and after “what” is also a verb. For example: Kirill, you only do what you have fun.
"What" connects parts of a complex sentence. For example: Only news that summer has come.

No comma needed

1. When "what" is a union or union word in the following situations:

If there are two or more homogeneous clauses in a complex sentence, which are connected by the conjunction "and". Sentences can start with different conjunctions, but must answer the same question. For example: Kirill knew how to save on food and what to cook for breakfast.
If the subordinate clause consists of only one union word. For example: Asya bought something for a friend as a present, but does not say what.

2. When "what" is an interrogative pronoun. In this case, it indicates the subject of the conversation, but does not name it, but helps to ask a question. For example: So what to do now?

3. When “what” is a particle that helps to express emotions. For example: What a punishment! What did you do?

4. When “what” is part of a stable expression. "Just now," "no way," "if anything." For example: You will never believe, but I just saw a deer. If anything, I'm not lying: here's a photo.

5. When "what" is part of a compound union. A comma is placed before the whole union - in all cases except those listed above. For example: Olga learned to draw because she practiced a lot.