Experience (often referred to as EXP) is the determining factor to upgrading your ship and buying a specific weapon.
You can earn EXP by completing campaign missions or PvP battle.Small percentage of the amount of EXP you get after battle are the amount of REXP that will you get.
Note:You can get more REXP by buying camoflauge.(not all ships have camoflauge)
Weapons will have 3 non-combat stats: Level of Unlock (LoU), Displacement (Weight), and Cost.
For more information of Displacement and Cost, check out the Weapons Article:
Level of Unlock is seen on a weapons page as "Level", but the page refers to LoU.
Ship Upgrades are unlocked at a specific level, and requires: Silver (in-game currency), Research Experience (REXP), and a specific amount of experience (not taken away).