https://meta.stackoverflow.com/feeds/tag/[insert tag name here]
Example: If there is a tag called "hotdogs" I can subscribe to that tag feed with the url:
https://meta.stackoverflow.com/feeds/tag/hotdogs
You can filter questions by tag by adding tags to you interesting tags list (that will provide highlighting for questions that come through matching your interesting tags). By clicking on a tag, you will be displayed a list of questions that match the tag you are looking for.
Another method is to use the search box and search for '[tag name]' (include the square brackets) and that will search specifically for that tag. Searching for '[tag name] my query' will search the questions for you query and limit the results only to those falling within [tag name]