Add the following line of code in
wp-config.php, just before the comment
/* That's all, stop editing! Happy blogging. */
/* Multisite */ define( 'WP_ALLOW_MULTISITE', true );
After the last step you should now see under tools ‘Network set up’
Remember to turn off all your plugins first, you can turn them back on once the multisite network has been created.
Fill in the appropriate details in the asked fields and copy information into index.php and .htaccess files as specified.
Click the ‘Install network’ button
After copying the relevant information you have successfully installed a Multisite. Now log back into WP-Admin, and take note that your header bar will display a different set of menu items.
Now you can see the list of multisite under the WordPress installation.
Click on Network Admin > Sites > Add Site, to add a new website to your network.