how to hear the effect live?

Sorry for such a newbie question -- I am using Sonar Artist with the guitar effect TH3 inserted at the top of the channel strip and I can hear the effect when I play my recorded guitar back.
 
How do I set up my channel strip so that I can audition the effects live as I am playing the guitar?  Thanks!

Click the input echo button on the track.

The Round trip latency of your audio driver will be shown in Sonars preferences under Driver settings. 
The audio driver quality is what determines the latency not the computers power. The computers processing power will allow you to use a lower buffer setting , that's all.  But many lower end interfaces have hidden buffers and your not going to get stellar latency performance. Example, the best I can get from my Scarlett 6i6 is a RTL of 9ms at the lowest buffer of 2ms. But it's pretty unstable at that setting, so it more happy at 5ms which jscks the RL back up about 12ms. So myself I can't use guitar sims live. 
Example; if I set my interfaces buffer to 128 I get a round trip latency of 17ms and that will be on both an old Duo core or and my i7. But the duo core can't be set any lower than that or it will drop out,  the i7 can go much lower without dropouts or stuttering.  
So if you do have a good interface and a good computer you might get your RTL down bellow 10ms which is workable. Above that you will start to hear a digital delay which might not have been the effect you were after. 

Nah... don't think it's going to be too high or it might be. :-)
 
Start with no effects on the track and just play. Get comfortable with it for a few minutes.
Next add your Amp Simulator. Most amp simulators are pretty efficient because the designers expect them to be used by musicians who are listening to the effect as they play.
 
Some effects add considerable latency because they look ahead at the audio to determine what to do with the audio currently. You will discover these yourself. Some offenders are...
Convolution Reverbs
Linear Phase anything
Some limiters with lots of look ahead
 
So use cheaper reverbs and eqs and you'll have an easier time with latency. When you are done recording, replace them with higher latency versions if you like.