If you are replacing a pane of glass, you need to make sure that you clean the tract in the muntins so you have a nice flat place for the glass to set in.
Tools and materials needed to do the job:
A small wood chissel seems to work the best for me, I use a small putty knife (about 1"), a small can of DAP 33 caulk, some points, and a small dish of water.
I clean the tract of the window with the wood chissel and make sure to remove the old caulk and points. (carefull not to remove the wood)
Then I take out some DAP 33 caulk and roll it in my hands like a snake. (When it becomes very plyable, it's done.) Using the putty knife, I apply a thin layer of caulk as a base.
I set the pane of glass into the tract and then placing the points on the glass, GENTLY, using the putty knife, slide the points into place.
Then, I again roll the caulk and place it at the edge of the glass. Using the putty knife, I draw the glazing against the muntin at the desired angle. I wet the putty knife every now and then to smooth the caulk. flip the window over and remove the extra caulk and let dry.
You could probably use caulk in a tube but, it's not as much fun! (remember Play-do?)