Hey Phalaer-

Not a stupid question at all! And welcome to the site!

There is no slam-dunk way to determine a strumming pattern for a song, but there are a bunch of patterns out there that you may begin to recognize when you start really listening for them. One in particular that shows up all over the place is one I call the "Classic Must-Know Strumming Pattern" (I'll include a link to a lesson on it below).

I recently posted a bunch of strumming tutorials that start from the very beginning, and work into more advanced strums. There are many more to come, as I plan to continue with the series and bring in all sorts of different, more advanced patterns.

Meanwhile, playing what you hear and feel "by ear" can be a really good way to go. One thing to watch out for though is that your strumming hand generally wants to maintain a steady down/up/down/up motion, no matter what the rhythm pattern is (assuming it's not way outside the box). If you find yourself contorting and tensing up in order to get at a certain groove, you may need to check to see if you can re-work your downstrokes and upstrokes.

Here are some links to my strum tutorials - let me know if this is helpful. BTW, the same principles apply whether you are playing acoustic or electric.

Intro to Acoustic Strumming I: Getting Started
http://www.guitartricks.com/tutorial.php?input=486

Acoustic Strumming II: Building on the Basics
http://www.guitartricks.com/tutorial.php?input=487

Acoustic Strumming V: Classic Must-Know Rhythms
http://www.guitartricks.com/tutorial.php?input=496

Best wishes - Lisa McCormick, Guitar Tricks Instructor