1) this is your own server, and you need to install these extensions
2) you webhost provides a cPanel that will allow you to install these extensions.
3) you will need to ask your webhost to install these extensions.
If you do not have the ZIP extension, you will not be able to use functions that read/write ZIP files.
If you do not have the INTL extension, webtrees will use a slower/less accurate algorithm for sorting text that contains accents and foreign characters.