The "5." is a numeric format. It says that the output field should have a width of 5. You should always look first in the SAS documentation instead of Google. To learn about the format, look in Base SAS: SAS Language Reference: Dictionary: Dictionary of Language Elements: Formats, for the "w.d" numeric format. Next learn about the "PUT function" that is using that format, by looking in Base SAS: SAS Language Reference: Dictionary: Dictionary of Language Elements: Functions and CALL Routines for "PUT function".
I may have been wrong to assume you have documentation available. Do you have anything? What do you get when you use the SAS Help menu? I am not much help if I tell you to look in documentation that you don't have.