To Do do multi site it says to open the wp-config.php

To Do do multi site it says to open the wp-config.php
above this line of code it says to put just as I have
The red code goes above. Then you save the file and backup your .htaccess file
Then go into admin area tool's and click on netwrok setup
If you use sites they will be in two differnet subdirectories.
Make sure you turn on wild card subdomains
in whm click on edit dns zone.
select the dns domain you want then click edit
The from the drop down put select A record.
put a star at the end of the big long box it should look like this * 14400 IN A IPOSTNAME

Here is the link to were the video is.

Then you have to edit the .htaccees file

Then you have to install.

The below script goes in the wp-config.php

define( ' WP_DEBUG' , false);

/* Multisite */
define( ' WP_ALLOW_MULTISITE' , true);

/* That’s all, stop editing! happy blogging. */

My main concern is how valuable is this multisite.
And what if you run into server problems when doing it.
Remember you are making changes to the server that's scary.
I have not had the best of luck with Linux although I have tried this I just forgot to make changes to the server and I received an error. What can multisite do.
I also have another head ache that's not wordpress.
It is a software php script that makes a domain registration site. I have done allot of work on this site I am running into SSL problems because all of the images need configuration with https I have done as best as I can if you look at hosting and click around and go back to hosting or other parts of the site you will see images disappear is there anyone who what this is. I have set everything to https although some images are not already set for https. I don't know how to do it.
I am going to have to let the company try to fix this mess. Any ideas they may hack me up.

Regards Vinny P.S Help