Understandable….an FTP is a program that you would install on your computer. Basically what it does is let’s you log into where your WordPress site files are and you can upload and download files with it. There are paid ones and free ones…the most popular free one is Filezilla (Client)
With your web host provider, you should have information about using FTP; info such as username, password, host address…etc. IF you are not sure what these are, you could submit a support ticket to them and get that information, but also check your host account documentation too.
Web hosts usually have a “File Manager” in the control panel that does the same thing, but it’s not quite as flexible as an FTP program, which is why I always suggest to people to have an FTP program.
If you still are not sure how this is done, go to the Support page on this site and at the bottom, click on Email Support. Send me your FTP information and I can use my ftp to upload the style:
1. ftp username
2. ftp password
3. Host address, usually it’s something like http://ftp.yourdomain.com but some hosts do it differently.