How do I subscribe to the tags that I am interested in?
I like to get notified via email or so, when someone asks new questions or if someone responds to my questions.
Mouse over the tag and you will see links to subscribe via email or RSS:
To subscribe to answers in one of your questions, there's a form at the bottom of the "Ask Question" page where you can request that:
In addition to what Anna correctly noted, you can also subscribe to a group of tags as a "Tag Filter" at http://stackexchange.com/filters
For an overview, see:
@RayLuo From what I saw on http://stackexchange.com/filters, you can add several filters to subscribe to multiple tags. See the screenshot: