In order to prevent people from making a huge number of unnecessary accounts, each account must have a minimum balance of 20 lumens (lumens are the built-in currency of the Stellar network). Since you don’t yet have any lumens, though, you can’t pay for an account. In the real world, you’ll usually pay an exchange that sells lumens in order to create a new account.
It goes on to say -
On Stellar’s test network, however, you can ask Friendbot, our friendly robot with a very fat wallet, to create an account for you.
So, on the main network, lumens need to be purchased at an exchange. On the test network, there is the bot. What should I use on my private network?