On VATSIM we have a rating system. Rating system determinates which positions you are allowed to controll all by yourself. Here is a small list to help.
OBS – none
S1 – ground (entry rating)
S2 – tower
S3 – approach / departure
C1 – area control
C3 – senior controler
I1 – instructor
SOLO VALIDATION – e.g. if you have S1 rating but have enough training on certain position, TD can issue a solo validation which allows you to control the position by yourself without mentor even though you don’t have a rating for that level of ATC. On this link you can find more details regarding rating requirements.