You can probably use this as a rough idea for your space forces. For ships, such as anything from corvette/frigate/destroyer (these being the smaller end of naval vessels, as opposed to service craft like fighters, shuttles, pinnaces, etc) up to the scale of battleships, dreadnoughts (even superdreadnoughts.. or larger!), the following scale is recommended.
Most naval forces are organized into a division at the lowest level, and a division is two to four ships (typically two or three at most). You would then have at least two, sometimes three and perhaps four, divsiions to assigned together into a squadron. Some navies may also call this a task group or task force, as well, but squadron would be the typical name.
Squadrons are then organized into task groups, task forces or groups depending on the hot naming trend of the time. Think of divisions and squadrons having tactical objectives, or supporting a strategic objective. Task groups/Groups/Task Forces are responsible for the strategic objective, such as securing a system or planetary system of lunar bodies, or something close to it.
Above the Group level you have your fleets, where there are a few groups working togehter for a strategic or national level of objectives - defend a sector/subsector or whatever.
Divisions are commanded by senior ship captain or a commodore
Squadrons can be the realm of rear admiral, vice admiral or even admiral if you like (it is, after all, your space force!)
Groups and larger are typically commanded by a vice admiral at a minimum. In my personal experience Groups are commanded by Admiral, while a fleet is the purview of a Fleet Admiral. And armada, or collection of more than one fleet with the same goal in mind, is typically under the command of a Grand Admiral.
Hope this helps - and don't be afraid to go with what you know or an amalgamation of what you know and the info provided here in this thread! Good luck and enjoy!