i have 2 colony ships can anybody plz tell me how could i discover and colonize new planets and how could i get metal and energy from these colonized planets

Send the colony ship to a vacant planet slot. If you have no idea what I'm talking about, then click 'Galaxy' in the player menu. See where you're planet is? The numbers where there are no planets beside are able to be colonized. Just switch between the 499 systems in each of the 9 galaxies, find a slot you are confortable with, and send a colonize mission.

On a side note, I wouldn't keep a planet with less than 300 fields. But you may want to start smaller if you don't want to waste time expanding your empire.