Mac OS on Macbook Pro running Windows.. Oh boy.

So, I've recently purchased a flawed Macbook Pro - It wouldn't turn on.

I ended up discovering it was due to a faulty HDD, which I changed to another running Windows 10 - And that of course worked.

Now, I'd very much like to install some sort of Mac OS on it (If you haven't figured yet, this is my very first Mac) and I'm quite clueless on where to begin. I often reinstall Windows or Linux on my stationary computer, but I've never dabbled in Mac before and from what I understand, it's quite a task.

Any tips?