Orange gear can be modded. That's good, as it means you can keep the same gear through your entire play on a character and simply upgrade the mods as you level. Orange gear comes in two varieties: regular armour (light, heavy or medium) or adaptive (which changes to suit the specific character).
Modifications can purchased for credits from planetary vendors or on the GTN. They may also be purchased for commendations from planetary vendors or vendors on the Fleet.
If this helps, I generally upgrade my mods and my companion's mods all at once using the fleet vendor every ten or so levels. It takes slightly less than 100 commendations to do that.
Or you can try to equip your character from items that drop as you do missions.