To send coins use the chat command "/send [steam64id] [amount]".
For example, to send 100 coins to steam64id 76561198160884702 you'd type "/send 76561198160884702 100".".
Alternatively right click the person's avatar in chat and select "Send coins.
To find your steam64id you can use sites like steamid.io
Coins are obtained by depositing CS:GO skins. If you've used up the free 100 coins you'll need to make a deposit to get more..DO NOT contact support asking for coins.
To generate your own referral code please visit the affiliates page located here. affiliates.