Login system script?

Hello! As a personal project of mine, I have taken to building a website that will allow users to register and log in with their credentials for access into the site. My only concern is that of security and whether or not any simple login script I pick up off the internet (like someone suggested I use instead of building my own) would be able to provide me a strong enough defense against any unlawful intruders.

I don't know how far my project will go or even if I intend on launching it officially. If I do however, I would like to know that I don't have to go back to the login system already implemented and replace the entire system (or modify it) to make it up to par against today's known vulnerabilities, hackers, etc.

I enjoy programming which is why I took up this project (to educate myself further and pursue this field), so I would love any advice from the experts in what you would do in my shoes. Thanks!

What programming language?