I have decided to study chess after playing it leisurely for a while. I looked at some online chess courses like the ones offered by Igor Smirnov at the Remote Chess Academy, but these options seem to be quite expensive ($700+). I looked at one of these courses that my friend purchased and it contained some openings that were annotated and showed variations of an opening: I was wondering whether there are freely available resources like the one in the picture below that have detailed annotations of openings, middle games, endgames, tactics, etc. If so, where would I be able to download them?
Alternatively, is there is any free/inexpensive software that acts as a trainer of some sort where one can practice openings, middle game strategy, end games, tactics, etc?