The "Enlisted crewmember" rank is the rank issued when you join the fleet. Enlisted crewmen don't get any rank picture until promoted to Ensign. Typically enlisted crewman are individuals who have joined our fleet through a game (such as STO) but nor formally joined via the forums. The rank of Ensign is given once the crewman has completed the necessary application on the forums.
Current Timelods enlisted crewman:
An enlisted crewman has essentially no powers.
Unlike the other ranks, an enlisted crewman has two options. He can become a Cadet and devote all his time to learning under a division member assigned to him, and get promoted to Lieutenant when the department CO feels he is ready, or try to get promoted to Ensign.