How to investigate an unknown method in powershell?

I'm learning Powershell by myself .There are tons of information around about the most common things, however when I'm faced with a slightly too specific thing, either I follow someone's previous steps or I'm lost. For instance, I don't know how to get help for specific methods. I'll give you my current situation as an example, however the question is about any case, not only this one.

I'm trying to automate some Internet Explorer browsing, and for that I'm using this guide. However it only shows an example on GetElementsByTagName. I already know how to use Get-MemberSo I follow his code like this:

$ie = new-object -ComObject "InternetExplorer.Application"
$ie.silent = $true
$ie.navigate($requestUri)
while($ie.Busy) { Start-Sleep -Milliseconds 100 }
$doc = $ie.Document

After that I use Get-Member -InputObject $doc so I know all possible methods and I see the one I need: GetElementByID. I try to use it like this:

PS C:\Users\Myuser> $main=$doc.getElementById("main")

Cannot find an overload for "getElementById" and the argument count: "1".
At line:1 char:1
+ $main=$doc.getElementById("main")
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : NotSpecified: (:) [], MethodException
+ FullyQualifiedErrorId : MethodCountCouldNotFindBest

I get that it expects more than one argument, but I don't know how to get or find any documentation about it.

What's your go-to when you want to know what a function/method does and what does it expect?