You've probably noticed that the way names for either variables and functions, or classes and methods can be cased differently. An easy thing to learn, but it's very important to choose only one way to define names in your project. Just so it's easier to maintain.
Usually, before a project, you define the specification of the project aka "specs" in what's called the project documentation aka "docs".
For example, Casing Styles or Capitalization Conventions, as defined by Microsoft for their .NET Framework, can be found here.
Be sure to check out other parts of their docs aswell, for guidance to see how Microsoft scale projects are built. Chances are, that all the time and money they've spent on polishing the process throughout the decades - they are probably onto something.
As you already see in the heading above, PascalCasing involves capitalizing the first letter of each word, another example - ThisIsPascalCased.
It seems to have originated from the Pascal Language.
This one looks like a camel. That's it. Wikipedia goes into more detail. In general you need to know, that it looks like a camel.
This one looks like a snake. No, really. It's just PascalCase with an underscore separating the words, rather than them being together.
Well, by now you can probably figure this one out too.
Those are just the most popular ones, there definitely are more out there to find, but regardless of which one you use, make sure that the whole team is on the same page!