On VATSIM we have a rating system. Rating system determinates which positions you are allowed to control 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 controller
I1 – Instructor
SOLO VALIDATION – e.g. if you have S1 rating but have enough training on a 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. Solo validation is last stop before your final exam (CPT) and in most cases, it is there to give the Training Department enough time to coordinate the date of your CPT and organize it. Solo Validation can be extended for a maximum of 6 months and after that, you will need to do CPT in order to work alone without a mentor. On this link, you can find more details regarding rating requirements.