Well, there are number of things you can do.  In the last step, try executing #agentdir#test.vbs instead c:\test.vbs.

But since you are just getting started, perhaps I can offer some helpful suggestions:

First, try using the procedure log to capture what is going on during the script.  I make extensive use of it in my scripts.  For example, the very first step in most of my scripts is a "Write Procedure Log Entry".  In in the box labeled "Enter the comment for the procedure log entry" I put something like this:

Starting script:  Test

After your first step where you create he variable, I would insert another "Write Procedure Log Entry" step that logs the value of the #agentdir# variable.  In the comment box, put:

agentdir variable = #agentdir#

Your "Write File" statement is fine, but I would drop the "Always True" statement.  It is not necessary.

I've never used the "Execute Vbscript" command.  I think it got added to Kaseya recently.  Try using the "Execute Shell Command - Get Results to Variable" instead with this as the command:

c: & cd #agentdir# & cscript /nologo test.vbs

Then add a step after it to write the resulting variable to the procedure log too.  Use this as the comment:

results = #global:cmdresults#

Finally, write a procedure log entry to indicate that the script execution made it to the final step.  Create one final "Write Procedure Log Entry" with this as the comment:

Script finished!