The 500 series are errors on the server; the remote computer that is “serving” that website to the internet. There are only a few things you can do to try to resolve it.
Where to host your website depends on what kind of a website it is. Options range from free to expensive based on your needs.
Not being able to access certain web sites isn’t that uncommon. Unfortunately there are many possible reasons.
The term “server” is used a lot in many contexts, but it’s really just a computer; quite often, it’s one that isn’t all that special.