The explanation pages on this website cover the big grammar topics, such as verb tenses, the articles, the passive. With such topics it is appropriate to use the words correct and incorrect. For example, it is incorrect to say: My father don't like German food or Do you have dog?
However, there are aspects of language where correct/incorrect are not the right terms. Consider the sentence: She is completely beautiful. Many native English speakers would say that the expression completely beautiful does not sound quite right; that incredibly beautiful or extremely beautiful sound better. But the expression is certainly not incorrect in the way that Do you have dog? is.
This aspect of usage (the expected combination of words) is called collocation. A grammarian would say that incredibly and beautiful collocate more strongly than completely and beautiful. There are no collocation rules that the student of English can sensibly learn. He or she must be prepared to use a dictionary in each case to find out about the expected word combinations, or to ask a native speaker.
An excellent modern alternative is to type the word combination into Google and see how many results are returned. In the example above completely beautiful got 36,100 hits, whereas incredibly beautiful got 861,000. It is very clear which is the stronger collocation (more common usage).