In your screenshot "TimeStamp" is an auto-complete and indicates what value you should put between the parenthesis.
Since you want the actual month, according to the actual time/date, you can make use of the expression .now within the Date plugin.
+ System: On start of layout
-> Text: Set text to Date.GetUTCMonth(Date.Now)
Will display "5" in your text object.
As indicated, the month is returned from 0 to 11 (0 is January, 1 is February, etc...).
If you want to display the month in "letters"/as word, you likely need to set up an array that contains your months and display it accordingly.
See this example c3p made in r201