Hey there!
Filezilla is a way of uploading stuff to your site. After you are done making some files on your computer, you need to upload them. If they are only on your computer, nobody can see them, so you need to get the files from your computer to the internet so that everyone sees they are there.
Filezilla does this. First, enter your host at the top left. This lets Filezilla know what website you are working on. For your site, it should be:
ftp.(put your site name here)
Next, enter your username and password. This is the same username and password you use to login to this site. This is so that nobody else can change your site around by uploading more files without you knowing.
Finally, put in the port. A port is kind of like a computer wire, in a way. A port always has one end plugged into your internet, and the other end plugged into where you want to connect to. So for example, when connecting to your email, you need a port. This port has one end connected to your internet, and the other connected to your email. Then that port, like a wire, takes the information from the email site to your internet connection. In this case, you want to use port 21, because that is the wire that is plugged into your site. So overall, the top bar in Filezilla should look like:
Host:ftp.(put your site name here) Username
put your username here) Password
put your password here) Port:21
Click the Quickconnect button and you will see many folders on the right side. The left side shows what's on the computer, and the right side shows what's on your website. You shouldn't tamper with most of the folders on the right side. There is only one folder you should change on the right side. It is called public_html, so double click on public_html. In this folder, you will see a file called index. Delete it for now, by clicking that file on the right side and then pressing the Delete key.
Here you must put your homepage. On most hosts, like this one, the homepage should be called index.htm, index.html or index.php . So if your homepage isn't called that on your computer already, rename it!
Now, in Filezilla, find the file you want to upload on your computer. Make sure you are in the public_html folder on the right side. Then, double click your file you want to upload, in this case, your homepage. If you get a popup message asking you to overwrite, click OK. Now see that green bar at the bottom? Wait until it fills. Once it dissapears, the file will be on your website!
If you just uploaded your homepage, go to your site and check that it works. If it does, start uploading more files to finish your website!
If you ever want to change a page on your site, change it on your computer then log in to Filezilla again, just like you did the first time. Then find the page you want to change on the right side and double click the page you want to change on the left side. If it asks you about overwriting, click OK. The new file is uploaded!
Hope it works!