Hello and welcome
To get the openssl/ssl.h header file I think you will need the libssl-dev package (the openssl package itself just contains the bits needed for running ssl - not for compiling)
There may well be other 'prerequisites' though - have a look in the downloaded driver directory and see if there is a README or INSTALL file that gives more detailed instructions than those on the website.
sudo apt-get install libssl-dev
If you want to take a step back and get help with your NIC driver in general, then I suggest posting a thread in the Networking and Wireless section where one of the networking gurus may be able to help you