I've got some songs ready to be rendered, but the music starts several bars in. I don't want silence at the beginning, and ending, of the tracks. How can I create start and end points for rendering?

Select all your tracks, then drag on the timeline. Selecting all tracks will go from start to song's end, but if you control click on the spot you wish to start/end, you can cut the excess off. HTH
 

Or you could insert markers at the start & end points of your song, Select All, open the Markers View and select/drag both markers

I also often have silence at the beginning of a tune. A song doesn't always begin on the first beat especially if there's a pickup drum fill. I just render it as is and trim the rendered file after the fact during the mastering step.

I use "Edit / Select / From here - To here
 
1- select all tracks then put NowTime line where you want the material to begin (a 1-3 second pre roll, what ever)
then go to Edit / select / from here.
 
2- Go to the end of said song and place the NowTime where you want the end to be.
then go to Edit / select / to here.
 
I think this area is one that needs better explaining in the Sonar help dialog / Sonar manual.
if you go to export audio in sonar help, it really doesn't discuss this in detail.
I would be one who supports a better explanation.

I used to mix my songs and burn CD's with no start or ending space.  I had a Radio DJ complain to me about that so I now have a 2 second lead in on the start of songs and about 1 second on ending.
 
 

I LOVE the special =START and =END markers in Reaper for this.  They totally eliminate the fiddliness getting ready for a bounce.

BobF
I LOVE the special =START and =END markers in Reaper for this.  They totally eliminate the fiddliness getting ready for a bounce.

Agree.
It has been feature requested numerous times.
We need special start/end markers in the marker menu for the purpose of exporting everything between the start/end markers. 

What Bristol_Jonesey said.
 
Using markers I get to keep my lead-in should I want to add more tracks later, but I reliably render the same start and length for as long as the project exists (or I decide to change the markers)

Brilliant, Bristol_Jonesey and jpetersen, it works!
 
Make a marker named "start" at the beginning, make a marker named "end" at the end.
Go to the markers menu and click on "start", hold the Control key and click on "end".
Everything in the time-line between "start" and "end" gets highlighted (regardless of any markers in-between).
 
Learn something new everyday.
I was always trying to select from the time line. I didn't know about the ability to select ranges in the marker menu.
 
Thanks!