Review the documents that you were served with carefully. In Civil Litigation you generally have 30 days to file an Answer with the Court. If you don’t file an Answer, you may lose the case by default.
If you are served with a Maryland lawsuit in another state and you live in another state, you have 60 days to file an Answer. If you are served with a Maryland lawsuit outside of the country and you live in another country, you have 90 days to file an Answer. There are other variations as well.
The worst thing you can do is ignore it!