What does % stand for in host column and how to change user's password?

The localhost means you can access from same machine while from % the remote host access is possible. The syntax is as follows to change the user password.

SET PASSWORD FOR 'yourUserName'@'localhost' ='yourPassword';

First check the user and host from MySQL.user table. The query is as follows −

mysql> select user,host from MySQL.user;

Here is the output −

+------------------+-----------+
| user             | host      |
+------------------+-----------+
| Bob              | %         |
| Manish           | %         |
| User2            | %         |
| mysql.infoschema | %         |
| mysql.session    | %         |
| mysql.sys        | %         |
| root             | %         |
| @UserName@       | localhost |
| Adam Smith       | localhost |
| James            | localhost |
| John             | localhost |
| John Doe         | localhost |
| User1            | localhost |
| am               | localhost |
| mysql.infoschema | localhost |
| mysql.session    | localhost |
+------------------+-----------+
16 rows in set (0.01 sec)

Now, let us change the password for user ‘John’. The query is as follows −

mysql> SET PASSWORD FOR 'John'@'localhost' ='John123456';
Query OK, 0 rows affected (0.35 sec)

After that you need to set the flush privileges. The query is as follows −

flush privileges;