Can not learn how to see posts on forum
You may have to join the group first. If you're not part of the group, there should be a blue "join" button on the group's page.
If you've already joined the group, then if you go to Groups (in the left menu), the group should be listed when you click My Groups. Click the group, and there should be a "new discussion" blue button on that page, with a drop-down arrow next to it that allows you to start a new discussion, ask a new question, start a poll, or announce an event.