There are quite a few different ways to find topics that interest you in the community. You can use the search icon in the top right hand corner or ask a question on the homepage of the space (ECM, App Dev, etc) that you're visiting.
If you're interested in seeing the most recent activity in a space, use the Activity tab.
This will give you a list of the newest activity - new discussions or blogs posted, new comments, documents updated, etc.
If you want to see ALL the content or narrow down the type of content you're seeing, use the Content tab. This will give you a list of all ECM content, regardless of type (blog, question, poll, etc).
You can then select the content type you'd like, or the category you'd like to focus on. You can also filter by action (marked helpful, marked outdated, etc) or by particular tag. Tags are free-text, so just start typing and see what comes up.