Ok,so basically my question is,if i get commendations from lets say ord mantell (starter planet for ranged classes on republic) can i use those to get end game material or what are they good for? can i only use them to get low level stuff or how do different planets commendations work??

Each planet has specific vendors that use their respective commendations.

 

Those commendations can not be used on any other planet.

 

So Ord Mantell can't purchase from Corellia, and Corellia can't purchase from Ord Mantell.

Your meant to use them as you level, to keep you topped up. Not save them until the end