Hi Tristan, welcome!

Good places to start are the About the site and the FAQ pages.

Browse the puzzles by the categories at the top, or the most recently posted ones all down the main page. A can add an answer or a question by clicking on the puzzle and then clicking "Post a comment" under the puzzle. You can submit your own puzzles with the Submit A Problem link on the right of the main page, but note that they take a few weeks to get through the queue.

Welcome again!