When first receiving a mission from star fleet via the hail option or in person.
Pressing "J" will bring up your quest log allowing you to select a mission of your choice and setting it as your current mission, now what you should do next.
Selecting you map will show you 3 option at the top of the map
:your current sector
:galaxy, in which every sector available within the game, this will also show you each system "eg" Risa, ceres and so on - so you can see were each sector is.
:Also a local list of every system in your current sector (all in alphabetical order) simple.
:Read mission in which it will specify an explanation and sector/system.
:Select you Map and it will show you your current sector map, follow map options above to locate correct sector or system
:Go to said sector using the above method and you will have no need to spam chat again looking for a system that is also in the same sector your in.
Failure to comprehend any part of the map system involved in this game would indicate that you still may be an undeveloped embryo.
Please feel free to mock me in anyway you feel comfortable with.
And continue to have fun in STO, above all else do not fail...