bitcoind deamon create new account for every user
Bitcoin-Core can manage different 'accounts'.
You can can create a new account by using 'getnewaddress':

bitcoin-cli getnewaddress "accountname"


If the account name exists, the address will be added to that account,
otherwise it will create a new account with that name.
You can see what accounts you have by using 'listaccounts'

For other options see: https://en.bitcoin.it/wiki/Original_Bitcoin_client/API_calls_list 

Note that these accounts are still considered part of a same "wallet", as it they belong to the same user.

If you want to separate them completely, you can run different instances by using different data folders.
Use the '-datadir=/path/to/data' option when running bitcoin (and again everytime you use 'bitcoin-cli') to tell bitcoin which "account" it has to use.

E.g.: 

bitcoind -datadir=/home/user/btc1/ -daemon
bitcoind -datadir=/home/user/btc2/ -daemon
bitcoin-cli -datadir=/home/user/btc1/ sendtoaddress &lt;address-of-btc2&gt; &lt;amount&gt;


Note that you can also use different configurations by placing different bitcoin.conf files inside each data folder.