It is easy to install but make sure your apache version is up2date just to avoid any errors.

First Need to build mod_gzip.

cd /usr/ports/www/mod_gzip
perl -pi -e Makefile 's/APXS=${APXS}/APXS=\/www\/apache\/bin\/apxs/g'
make
make install clean

If you receive any google it but i have not received any error in at least 50 times.

Make sure you enabled mod_gzip in httpd.conf.

| httpd.conf

LoadModule gzip_module        libexec/mod_gzip.so

Than enable following variables on your Directory variable.

| httpd.conf

mod_gzip_on Yes
mod_gzip_can_negotiate Yes
mod_gzip_static_suffix .gz
AddEncoding gzip .gz
mod_gzip_update_static No
mod_gzip_command_version      '/mod_gzip_status'
mod_gzip_keep_workfiles       No
mod_gzip_maximum_file_size    500000
mod_gzip_maximum_inmem_size   60000
mod_gzip_min_http             1000
mod_gzip_handle_methods        GET POST
mod_gzip_item_include         file       \.html$
mod_gzip_item_exclude         file       \.js$
mod_gzip_item_exclude         file       \.css$
mod_gzip_item_include         file       \.pl$
mod_gzip_item_include         file       \.php$
mod_gzip_item_include         handler    ^cgi-script$
mod_gzip_item_include         mime       ^text/html$
mod_gzip_item_include         mime       ^text/plain$
mod_gzip_item_include         mime       ^httpd/unix-directory$
mod_gzip_item_exclude         mime       ^image/

Now go to following links and test if it works.
If not check error_log.

- From Microsoft - What is my ip