Well, to be more precise than anything I’ve seen so far…
If you file criminal charges against a person for any of the various things that are statutory crimes: theft, fraud, assault, threatening, etc., then the District Attorney will evaluate the charges, mount an investigation if warranted, and if a case can be made the DA will make the state’s criminal case. In that sense the DA “represents you”. (Actually, the DA represents the state’s interest in maintaining law and order, and for that reason the DA may modify the charges – or drop them entirely if he wants the person’s cooperation in prosecuting “bigger fish” – make plea deals, etc. without consulting you, because he’s not “your” lawyer.)
If you file civil charges against someone for “wrongs done against you” which may not rise to the level of “criminal offense”, then you’ll want an attorney to make that case. Any decisions to be made as to charges filed, evidence (of yours) to be presented, and how or whether to prosecute the case or make a settlement agreement with the defendant will be discussed with you, because you are the one engaging the attorney’s services and he takes his orders from you. You don’t actually “need” an attorney here, either – unless you really want to win the case!