For newbie, hit level 3 and complete the first quest to unlock womb pregnancy.
Then head to any planet and start mating with aliens using "seduce" and "pussy seduce" skills.
Once Sasha is fertilized, get back to the ship and sleep a few times to breed your first offspring.
Go back to the planet and mate with the same type of monster until Sasha is preg.
If you get the same type of offspring again, you will get an "Unknown Creature".
After that, craft a "(Lab) Disintegrator" at the assembly bay on the bottom right side of your ship.
This item will enable the Disintegrator function on the bottom left side of your ship.
Now you can sell "Unknown Creature" with 50 Bytes each.
More information for you:
You can use Sasha skill "Change Partner" to switch offspring anytime.
Craft "Hormones Spray" to attract enemy attack on targeted teamate if you want.
Offspring can only breed "Unknown Creature" so far, assign a pregnant offspring by your side during sleep will accelerate their growth.