I have x4 adv. planet discovery items.
When I click on it I get the pop up for use adv. planet discovery.
When I click ok I get you my st level up to colonize more planets. After your get your second planet at level 20 the number of planets you can colonize increases by 1.for every 10 levels.
I am currently at level 44. At the start of the game I believe I skipped the last instruction set to try and get me to colonize a 2nd planet.