so my website pretty much is "hi" in index.html (two characters) and I got a "D". so to help me understand how to hack this installation, how can I use the webs

so my website pretty much is "hi" in index.html (two characters) and I got a "D". so to help me understand how to hack this installation, how can I use the websites evaluation to hack into it so I can understand the exploitation of the security holes I have obviously left open? Is there any guidance here?