As Scook already pointed out, you don't want to only put sound INTO Sonar, you want to get it out too. You need to hear what you've recorded and you need to hear what you're playing. In other words, you need an audio interface. At a bare minimum you need a stereo output and a guitar input. Honestly the halfway decent devices start off around 150 to 200e new in the box. If you can't spare that right now I would save up, crowdfund amongst friends and family or whatever. You may have a disappointing experience otherwise.

 
The headphone out may be quite sufficient for ajbowler's needs.  If funds are tight there probably aren't any for active monitors that would be needed in addition to an interface.  That's about 350-400$ minimum, total.
 
The Behringer maybe be enough.  Latency will probably not be super low and I read of some possible low level hiss, but it would certainly be better than nothing.
 

The unit you reference is not a USB adapter it is a specialized audio interface. The good news is that they say it will work with Audacity and that it has an ASIO driver, so likely Sonar will recognize and communicate with it. It is also limited to 16 bit audio, which is somewhat limiting, and it is not at all clear what the included processing software is or how it will integrate with a DAW. If you just want to record your own guitar playing, the smart move would be to use Audacity (no cost) and spend the money you would spend on Sonar on a general purpose USB audio interface instead. The unlimited tracks, deep processing power, MIDI capability etc. of Sonar is not going to be something you will need or be able to exploit fully with the single guitar interface. 

slartabartfast
...It is also limited to 16 bit audio, which is somewhat limiting...

 
Not only that, but the sample rate is fixed at 48kHz too.

I would recommend a Line6 GX instead.
http://line6.com/podstudiogx/
 
 

Having experienced the path you seem to be on first-hand, the advice above about getting a real audio interface will save you significant grief on "trying to make bad things work." Depending how much you get into things, introductory gear is more a stepping stone to replace with better as your needs change/grow over time. If you are satisfied with where you are for long periods that is also great, but not if struggling with something not "right" for the job.
 
There are a handful of sub-$100 interfaces (new) out there. Not "stellar" but functional for overdubbing (one track at a time) purposes. If you are looking to also do vocals (potentially), an interface with one microphone pre-amp is also useful. Definitely worth consideration. The 16bit/48KHz recording limitations mentioned above may end up causing you grief down the road.
 
Before jumping into "buy this, get that" mode... what are your goals for recording?
 

If cost is a limiting factor, the ALESIS Core 1 USB Audio Interface is cheaper, although fixed @ 48K.
 
Alternatively, the Lexicon Alpha Studio USB Audio Interface is only a tenner more (~£40 on Amazon), and is a much better interface than the Behringer one (it's 50% off atm).  Comes bundled with Cubase LE too.

Another alternative would be Roland Duo Capture Mk2, which comes with Sonar X1 LE, for around 55GBP in the UK (Your price is probably lower as I am guessing that you are not in the UK).
 
Although the specs state two inputs, in practice, you can only use 1 guitar or mic directly at a time, but that limitation is common to the lowest cost decent quality interfaces.
 
Sonar X1 LE is not the most up-to-date Sonar, but it gets you started pretty effectively and it is free.

 

ajbowler

57Gregy
There is no right 1/4"-to-USB adapter.
Get an audio interface that supports ASIO and has guitar and mic inputs.
Welcome to the forum!

Thanks for the advice! I'm going to hold off on buying a full audio interface as those can get expensive and I'm just a student in college, so I'm looking for a simple cable for my guitar to hold me over.

 
Get yourself an inexpensive USB 2.0 Audio/Midi interface as you will be using midi later on... I guarantee  it. 
 
Check Craigslist and buy a used one.  
 
 

Jesse G
 
Check Craigslist and buy a used one.  
 

FWIW here in the UK, Ebay is the market place of choice and the peculiar phenomenon is that second-hand interfaces by Roland, Focusrite and other respectable vendors seem to go for prices that are nearly as high as the current street prices. Why that is, I do not know (as I would rather pay the street price to have the warranty rather than save a few percent). However, I have taken it as a general rule that any interface that holds its price on e-bay is reliable and good - any that doesn't is likely to be obsolescent or troublesome in some way. Just saying!
 
The good news is that it is relatively inexpensive to try out a given product and then sell it on if it is not what you want in practice.