Welcome from central Florida. Above the post you will see Bookmark - click on it and a little "thing" will appear, there is a place for a reminder as to why you bookmarked it and then click on Save. Right at the top of the page you will see "My Bookmarks" and that is where you can find them again.
When you click into a topic, at the bottom of the page you will see "Quick Reply" - write whatever you want, decide if you want to follow the topic (if not, take the check mark out of "watch this topic" and then click on Send.