GZIP compression is used for compressing the content of the web pages by the server before the content (text & images) get passed to the browser. The browser takes this input and decompresses the content before delivering it to site users.
Compressing the content of the pages makes the page size small which in turn will have a positive & significant impact on the page loading. There is a misconception that the larger bandwidth availability or lesser file size is what is needed for faster page loading, which is not.
In .htaccess: to gzip output before delivering the content
# Compress some text file types
# Deactivate compression for buggy browsers
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0 no-gzip
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
If you are a beginner into Linux, there are chances that you might research on the web to see why...