Many people were ruined at school, by faultless teaching, when grammar was blurred for several years.

I will tell you as an old translator of technical texts - over the years of work I have had the impression that the native speakers themselves DO NOT KNOW all these subtleties of English grammar. Some grammatically wise sentences in technical literature that are disappearing rarely found in modern literature (that is, if the native speaker, especially an American, wrote it). Learn the words, kids. Many words, good and different. Read books, watch movies. Active knowledge of the language will not give you, but in a live conversation you can always ask (unless you are a translator). Grammar... let it go! The English grammar is one of the simplest, with no comparison to Russian. honestly honestly.