You can file and get separated on your own with out hiring an attorney. The first thing you will need to do is make sure you have a certified copy of your marriage certificate to prove that your were legally married.
You can get a copy of your marriage certificate at the local town hall in the town you where married in. There is usually a fee associated with this and it can be done by mail. The next thing you will need to do is locate the local Probate and Family Court in the town you live in or last lived as a married couple. Once you locate the Court you will need to call or go to the court and ask for the forms you will need to complete to file for a Legal Separation. I always suggest going in person so you have a person to talk to if you have a question or concern.
Once you complete all the forms required return them to the Court and file them Once they are filed you will get a court date and will have to serve the other party a copy of the forms you filed and inform them of the court date. It is your responsibility to serve the other party the forms NOT THE COURT! You will need to locate a constable or Sheriff, pay them and they will serve the other party they forms. So yes you need to know where the other party lives or works. If you do not have this information at for help at the Court you may have to publish something in the newspaper. Once the other party is served and you have your court date you are already to go to Court. Rememebr separation is no divorce but you can still request child support and help paying the bills or mortgage on a home.