1) The first step is to create a wallet and possibly a custom token to distribute. Those instructions are here:
2) Once your wallet is created at burnerfactory.com, go to Distribution in the top menu, then select New Account Set.
3) Name the Account Set. This is for internal usage only, choose a name so you can identify the set. Press NEXT to continue.
4) Increase (+) or Decrease (-) the number of accounts (wallets) you want to generate. Keep Save to LocalStorage checked, and press DOWNLOAD BACKUP FILE to download a JSON file containing addresses and private keys. Click Save and Close.
5) You will return to the main Distribution page, and see your new Account set generated. Click on the account set name you just created.
6) Next you will have several options. You can print/download paper wallets, or add assets to airdrop to each address. These can occur in either order, although if you are distributing to individuals immediately (and you want tokens or xDai included on a wallet) you may want to airdrop first.