Simple rules for gearing until you reach level 50 is to do daily flashpoints for both gear(if lucky) and planetary commendations. There are several daily missions that can be picked up at the priority mission terminal on fleet(supplies). This will essentially give you all you need to gear your characters up from level 11 to 49.
But as said previously f2p and prefered players can generally not use artifacts(purple gear) unless they have bought the [Artifact Authorization] from either the Galactic Market or Cartel Market.
In my opinion though, you don’t really need artifact gear(purple gear) to stay ahead of where you’re leveling. The blue mods sold by the planetary vendors at fleet or the modification vendors on the various planets will do just fine.
If you just get a set of customizable gear and change those mods, armorings and enhancements about every 5 levels you should do fine.

It costs 96 planetary commendation until level 50 to change all mods, armorings and enhancements in a fully customizable gear set. So another good thing is to get 96 of those commendations and then change your gear, but keep in mind that on the higher levels you might need to change this more often if you are dying a lot.

Note: Flashpoints are also a good way to get to know the class you are playing and checking out the different talent trees at the disposal for your class and some of these flashpoints get a hard mode version on level 50+. Which also helps you know the flashpoints when you start getting into the harder content. Also being a damage dealer is the worst possible way to gear up in a flashpoint unless you can find a group willing to help you. Tanks and healers are sought everywhere and needed almost all of the time, but not everyone wants to be a tank and healer of course. Then we have the tactical flashpoint KDY(Kuat Drive Yards) which is boring, but helpful I guess.

Will post more on specifics for the various roles(tank, healer and dps) you can fill in a flashpoint and operation statwise and such.

PS: Have fun while playing otherwise your gearing won’t make any difference in the long run. 😉