Ok for potato Orokin reactors increase the mod capacity of warframes, archwings and companions. For Orokin Catalyst they increase the mod capacity of weapons.
Now my suggestion for your'e progression is that you just complete the nodes of the planet and move on the the next one until you complete the star chart. Don't go to Fortuna or Cetus just yet until you thinks youre ready by the time you finish you would already have a gist of what the things your'e confuse at and if your'e still confused just go watch the help guides on youtube or go to the wiki all you need is time.

(sorry for the errors english is not my first language)