1. Install WordPress
2. Open wp-config.php file
3. Find out this line:
/* That's all, stop editing! Happy blogging. */
4. Add this code before this (3) comment:
/* Multisite */
define( 'WP_ALLOW_MULTISITE', true );
5. Now refresh the WordPress dashboard.
6. Go to Tools option
7. You will see a new option there named Network Setup
8. Click Network Setup and install the network
9. After that you will get two codes.
10. Copy the first code and add it in wp-config.php file before this comment:
/* That's all, stop editing! Happy blogging. */
11. Add the second code in .htaccess file
# BEGIN WordPress
//add your code here
# END WordPress
12. Now you can add multiple site under one WordPress Install.