In my effort to keep my brain warmed up for poker, and hopefully be able to win a game of chess at the local café now and then, I signed up for online chess at Lichess, which is a popular free and open source chess server, that is driven by volunteers and donations. You can play chess on the homepage or in the smartphone app.
Lichess offers a study program, computer opponents and games vs. friends and other registered chess player opponents. You can review your games, get tips for improvements of your strategy and explore the database of known chess openings.
Feel free to visit my profile, follow me (for friendship) and challenge me for a nice game of chess. I am registered as Micski. I have not played chess since my childhood, so I would estimate my knowledge of chess openings and moves to be at the lower rank. I wrote a little introduction to Lichess and an introduction to chess openings.