Take a deep breath. If the case is proceeding by way of summons, then there is no arrest warrant. What probably happened is that the Sheriff tried to serve you, but were unable to do so at the address they had listed.
I recently had a client who also had to appear at the Sheriff's Office to pick up a DUI/DWI summons.
Basically, the summons is the official district court charging document. You will receive your summons for court and other paperwork: statement of charges and notice of attorney. You will be released and receive a court date. This starts the process of having a Maryland DUI/DWI case set for trial.
Once you receive your paperwork, contact a Maryland criminal defense attorney and schedule a free consultation.