Use get's account command to manage accounts, such as creating new accounts, updating account passwords, querying accounts, and so on:

geth account <command> [options...] [arguments...]

Command-command

List list shows existing accounts
 NewCreate a new account
 update Modify Account
 import Private Key to Create New Account

You can use--help to get help information for these commands, for example:

~$ geth account list --help
list [command options] [arguments...]

Print a short summary of all accounts

OPTIONS:
  --datadir "/home/bas/.ethereum"  Data directory for the databases and keystore
  --keystore                       Directory for the keystore (default = inside the datadir)

Create a new account

Use the geth account new command to create a new account:

$ geth account new
Your new account is locked with a password. Please give a password. Do not forget this password.
Passphrase:
Repeat Passphrase:
Address: {168bc315a2ee09042d83d7c5811b533620531f67}

Import private key to create a new account

You can create a new account by importing the private key using the geth account import command.

~$ geth account import --datadir /someOtherEthDataDir ./key.prv
The new account will be encrypted with a passphrase.
Please enter a passphrase now.
Passphrase:
Repeat Passphrase:
Address: {7f444580bfef4b9bc7e14eb7fb2a029336b07c9d}

Update account password

Use the geth account update command to update the password for the specified account:

~$ geth account update a94f5374fce5edbc8e2a8697c15331677e6ebf0b
Unlocking account a94f5374fce5edbc8e2a8697c15331677e6ebf0b | Attempt 1/3
Passphrase:
0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b
Account 'a94f5374fce5edbc8e2a8697c15331677e6ebf0b' unlocked.
Please give a new password. Do not forget this password.
Passphrase:
Repeat Passphrase:
0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b

Show existing accounts

Use the geth account list command list to display the existing accounts, optionally specify the keystore directory with --keystore:

~$ geth account list --keystore /tmp/mykeystore/
Account #0: {5afdd78bdacb56ab1dad28741ea2a0e47fe41331} keystore:///tmp/mykeystore/UTC--2017-04-28T08-46-27.437847599Z--5afdd78bdacb56ab1dad28741ea2a0e47fe41331
Account #1: {9acb9ff906641a434803efb474c96a837756287f} keystore:///tmp/mykeystore/UTC--2017-04-28T08-46-52.180688336Z--9acb9ff906641a434803efb474c96a837756287f

Original: Guide to get account management