If you have any old or poorly sealed windows, you may need to caulk them. Caulk prevents drafts and keeps moisture from entering, which could cause the paint to peel or the wood to rot.
Step one is to gather your tools, a putty knife or scraper, utility knife, a long nail or wire hanger, a tube of caulk, which is generally enough to caulk around an average sized door or window, a caulk gun and a small plastic spoon or ice cream stick. The caulk tube fits into a caulk gun. The gun has a trigger handle that you squeeze to apply pressure to the tube, forcing the caulk out of the nozzle.
To seal a window with caulk, whether inside or out, the second step is to use a putty knife or scraper to clean away any old caulk.
Step three is to cut the tip of the caulk tube nozzle right near the end at a point where it produces a bead large enough to fill the crack. A quarter inch bead is large enough for most cracks. If you need a large bead, just cut it further down the plastic nozzle.
Step four is to puncture the seal in the end of the caulk tube to make the caulk flow. To do that, insert the nail or the end of the hanger into the nozzle, push into the caulk tube until you feel it puncture the seal.
Apply the bead of caulk, moving the caulk gun at a measured pace along the crack and using continuous light pressure on the gun trigger. Caulk on all four sides of the window to seal the crack.
Step six, smooth the caulk with a plastic spoon, ice cream stick or your wet finger to create a smooth surface.
Finally, wash away all the remaining caulk on the caulk gun, your hands or other spots before it dries. You now have a nice, air tight seal.