These descriptions are for the Civilians, which is represented by the color white. Civilians generally do not answer to any formal chain of command, but Starfleet has the role of protecting them in times of crisis or combat. Some of the more common civilians that you will find around Starfleet facilities include the following.
On almost every Starfleet vessel and base, there is some kind of recreational area. A place where all members of the crew can relax and enjoy, a place to forget the rigours of the day.
The Bar/Lounge Manger runs such establishments for the crew.
A ship/facility is operational 24 hours a day, and thus people are on duty around the clock, each having there free time at different times, but the recreational areas must stay open to accommodate these people. A Bar/Lounge Manager could not keep going 24 hours every day, and thus requires staff to assist him/her. A bartender does just that, dispensing drinks to those that happen by the bar.
Every bar, every restaurant needs some form of friendly service to help the crew relax. A warm smile who brings your food or drinks, to chat when somebody is alone or down. the Water/Waitress are theses people.
In the modern 24th century, many children are taught by computer holograms. However real interaction with a living person is still valued. A computer can only teach so much. The teachers responsibilities is the education of the children aboard the ship/facility.
Additionally the teacher may be able to provide assistance in his/her field of specialty when required.
In the modern 24th century, many people still need to get hair cuts. This can be done by more, modern means, however real interaction with a living person is still valued. Besides, like the bartender, a barber is a good place to get advice, get something off your chest, or just talk about 'scuttlebutt' or gossip.
Additionally the barber may be able to provide assistance in his/her field of specialty when required.
Many of the Federation's top minds and specialists in different fields aren't in Starfleet, they are civilians. These people often venture into space aboard Starships and other facilities. They maybe Doctors, Scientist, or even Engineers. They use some of the science labs, when possible, to do their work while not interfering in operations of the ship or facility. Starfleet's primary role is exploration, and having these people on board really helps that endeavor.
A Commissioner is a direct representative of the Federation Council (or one of the sub-councils, for example, the Federation Science Council), with authority derived from the government. As a direct reprsentative of the government, a Commissioner has expansive power under various Federation laws and treaties, with varying levels of power, dependent on how the Federation Council has empowered said Commissioner. A Commissioner may have power over an individual research area, or may have power over a city, district, province, planet, sector, parsec, relief and diplomatic mission, starship or even a starbase (including personnel). Commissioners may have judicial powers as well, and some have the authority to override the Commanding Officer of a ship or base.
There are various levels of Commissioner, the senior level being a Galactic High Commissioner. Other levels include High Commissioner, Commissioner and Assistant Commissioner. Other levels may be created as necessary by the appropriate governmental agency.
Examples of types of Commissioner:
In 2267, Galactic High Commissioner Ferris, ordered the USS Enterprise Captain (James Kirk) to abandon a search of the shuttlecraft Galileo in order to head to Makus III to deliver medical supplies. His authority came from Title 15 of the Galactic Emergency Procedures.
Also in 2267, Federation Assistant Commissioner Nancy Hedford was sent to Epsilon Canaris III on a diplomatic mission to prevent a war. Commissioner Hadford also ordered Captain Kirk to comply with her orders to repair the shuttle so she could complete her mission. Due to there situation, and Hedford's illness, Kirk was not able to follow her orders. Hedford eventually merged with a non-corporeal alien and stayed on the planet the shuttle had crashed on.
When the Dohlman of Elas and the Troyian Head of Stated were to be married in 2268, a High Commissioner was scheduled to attend the nupitals.