How To install php extension

How to install these extensions

OpenSSL (PHP Extension)
Mysqli (PHP Extension)
cURL (PHP Extension)
GD (PHP Extension)
Mbstring (PHP Extension)
Zip (PHP Extension)
GZip (PHP Extension)
Exif (PHP Extension)
DOMDocument (PHP Extension)

apt-get install php-exstension

apt-get install php-gd

Should work

Mysqli is part of Mysql extensions (Should be installed by default)
php-gzip doesn’t exists
domdocument = php-xml
gzip = zlib

php-curl
php-gd

You need to install the specific extension for particular PHP version. so first identify which PHP version you are using, then do apt install php7.x-gd and so on