Human-Reader Aspect

The lines of code inside the block are indented four spaces. This is an extremely important concept. It's not important for the script engine that these lines be indented, but for humans who are reading your code, proper indentation is especial. The script engine does not care whether your code has a pleasing appearance, or even that the visual presentation make any sense at all. For example, the following script is completely legal and will execute just fine:

Dim Greeting
Dim UserName
UserName = InputBox("Please enter your name:")
If Trim(UserName) = "" Then
Greeting = "Why won't you tell me your name? That's not very nice."
Greeting = "Hello. " & UserName & ", it's a pleasure to meet you."
End If
MsgBox Greeting

This might be fine for the script engine, but it's a nightmare for you and your fellow programmers to make sense of. Generally, you need to indent your code whenever a line or series of lines is subordinate to the lines above and below it. For example, the lines after the IF clause and the Else clause belong inside the If...Else...End If block, so we indent them to visually suggest this.

This points up a very important programming principle: the presentation of your code should visually suggest its logical structure. In other words, without reading it, we can look at the code and, consciously or unconsciously, getting sense for how it is organized and how it works. By detecting the indentations inside the If...Else...End If block, we can "see" the branching logic at that point in the code, indenting is only one element of programming style, but learning and following styled layout is essential for any programmer who wants to be taken seriously.