Basic Upload Using VBA - vba

Question

I am trying to understand the file upload process using vba and winhttp.
I am trying to upload files to:
https://uploadfiles.io/
Using the following code in VBA:
Public Function GetFileBytes(ByVal path As String) As Byte()
Dim lngFileNum As Long
Dim bytRtnVal() As Byte
lngFileNum = FreeFile
If LenB(Dir(path)) Then ''// Does file exist?
Open path For Binary Access Read As lngFileNum
ReDim bytRtnVal(LOF(lngFileNum) - 1&) As Byte
Get lngFileNum, , bytRtnVal
Close lngFileNum
Else
Err.Raise 53
End If
GetFileBytes = bytRtnVal
Erase bytRtnVal
End Function
Sub testLoad()
Dim http
Dim filedata() As Byte
filedata = GetFileBytes("C:\apps\somefile.pdf")
Set http = CreateObject("WinHttp.WinHttpRequest.5.1")
URL = "https://uploadfiles.io/upload"
http.Open "POST", URL, False
http.setRequestHeader "Content-Type", "multipart/form-data; boundary=---------------------------7e1881e4703b8" 'Add boundary
http.setRequestHeader "Content-Length", 80047 'Add length
http.send filedata
MsgBox http.Status
End Sub
I am a pretty big noob working with the web and winhttp. Using this code I get a successful 200 response... I think. But I have no idea where the file is now that it is uploaded. So here are my questions:
1.) Where and how do I set the file information as it is being uploaded?
2.) What exactly is the "boundary=" in the requestHeader? I manually set this by watching the network traffic, but I don't know what it means.
3.) What is the length in the requestHeader? Can I use len(filedata)
Any help would be greatly appreciated, thank you.