Trying to cut with a dull chainsaw blade not only takes longer but also can be dangerous. You should not have to push the chain through the wood---the chain should act like an automatic can opener, pulling itself through the cut. You can always check when your chain needs sharpening by paying attention to the woodchips thrown off by your saw: small chips or fine dust usually indicated that it's time to sharpen the blade on your McCulloch saw.
Turn off the saw. Pull the black front hand guard toward the front handle to make sure the chain brake is disengaged. Set the saw onto a flat area to sharpen the chain.
With a gloved hand, spin the chain around and look for the tooth with the most damage, such as heavy nicks or gouges. You'll want to file every tooth evenly so it's important to select the tooth with either the smallest amount of top plate left or the one that will need the most sharpening.
Position your body parallel to the bar. Grasp the bar with your non-dominant hand and hold it still. Set the tip of the correctly sized round file into the tooth you selected as your starting point. The size of your chain will dictate what size file to use; the size will be on the box the chain came in, or it may be stamped onto the bar.
Hold the bar still while pushing the handle of the file all the way to the tooth. Watch your angle; use roughly a 60-degree angle to the engine or the guide marks on the top plate of every tooth. Steady the file as you push it across so it always stays parallel to the ground. Don't pitch it up and down while sliding it across the tooth.
Swipe the tooth with fast and even strokes, counting each stroke used. Keep filing until the angle on the tip has been restored and the gouge marks have been removed. Pull the chain up two teeth so the next tooth you sharpen faces the same way. File the next tooth in the exact same manner, trying to grind it down smoothly and even to the first.
Repeat the filing steps for every tooth on the same side. Then, flip the saw around and repeat the steps for the teeth on the other side.
Always try to grind each tooth in the same manner, with the same angle and the same number of strokes, which will greatly improve cutting performance. Correct filing techniques takes a bit of practice.