Lineage societies decide their members based on the activities of ancestors who lived in a specific period. For the Society of Colonial Wars and other colonial societies, a commissioned military officer is considered to be a qualifying ancestor. That means if your direct ancestor served as a commissioned military officer, you are likely able to join the society.
There are limited ways an ancestor could have served in the military. The United States didn’t have a Navy for most of the colonial period: the first “Navy” was established in 1775. The United States also didn’t an Army until 1775. Prior to that date, British units were brought into the United States as needed. (Provincial army units were temporarily formed during the French and Indian War, but they were second to the British Army.) For most of the colonial period, the main place an ancestor could have served as a commissioned military officer was in the militia.
Militia ranks were brought into the formation of the Continental Army. There’s a great explanation of those ranks here. Many will be familiar. One likely will not. The ensign, the lowest of the commissioned ranks, was abolished in 1815 and is no longer used by the Army.