Depends on your audio interface. Yes, you do have an interface, it's just built onto the motherboard. There should be a microphone input for it, which
might work OK (but probably not great) with your guitar. You'll just need a 1/4" to 1/8" adapter to try it out.
You'll get better results by using the interface's line input, with some kind of amplification stage before it, such as a mixer or preamp. Or, if you're using a guitar amp that has a line out, you can use that. Note that the line and mic inputs (and outputs) look the same, and on many computers may not be labeled. Try them all and see which one works.
No matter how you finagle it, you'll probably not be thrilled with the results until you add a proper external audio interface. But don't let anybody tell you that's an absolute requirement. The plain old integrated audio will suffice, at least as the gateway drug until you're bitten by the recording bug and start emptying your wallet on a regular basis.
When you create an audio track in SONAR, you'll have to specify where the sound is coming from. There will be a dropdown list (labeled "I" for "Input") that should include your audio interface's mic and/or line inputs.