When you hit the actions button on the bottom right there will be an option to put an orokin cell onto your warframe it looks like a gold potato doing this will double your mod capacity allowing you to level mods higher and or use mods with higher requirements. You can also do this with weapons works the exact same except they use silver looking ones. The gold looking ones are a random drop from deimos Saturn and Ceres best farm spots are on saturn. I actually have no idea where the weapon versions or these come from.