The most you will feel is like a small pinch as the needle is tapped in. Most people don't feel anything at all. Once the needle is tapped in, then it is manipulated to get a mild 'Qi' sensation. This feeling is different for everyone and depends on the time of day, the season, level of relaxation, if an illness is present or not, etc. Usually people describe it as a dull, heavy sensation or a tingling sensation that follows the acupuncture meridians. As one of my 12 year-old patients says.. 'it feels cool!..'

Traditional Chinese Medicine (TCM) – works by keeping the body in balance.  Our bodies are complex systems made up of flesh, energy (Qi, pronounced ‘chee’), blood, and essence.  In reality, everything is made up of various forms of energy (Qi).  This can be a confusing subject to grasp, but it’s interesting to note that in western physics matter is made up of electrical particles (atoms) joined by electromagnetic bonds.  This electrical concept of the universe was known by the Chinese over two thousand years ago!  When the various substances flow smoothly through the body, we feel healthy, happy, and mentally balanced.   When this circulation becomes disrupted, then disease will result if harmony isn’t restored.  Our bodies are always trying to return to balance, but sometimes we do things that get it out of balance, or the environment changes and causes disharmony in our Qi.  For example, if someone eats too much fatty food, they can gain weight.  When the weather changes during changing of the seasons, colds abound.  If someone can’t resolve a sad situation, depression can result.  These are examples of things that can cause imbalance in the body.  When imbalance occurs, TCM can help restore you back to a balanced, healthy state.

There are many tools of TCM that are used to restore health.  The most widely and best known is the acupuncture needle.  These are very fine needles that are inserted into acupuncture points along pathways of energy flow on the body.  Other therapies include herbal formulas, suction cupping, channel scraping, and moxabustion.  A practitioner of TCM will discuss the various methods with you that they feel are appropriate to treat your condition.

There's another detailed description at Acupuncture.com that may be of interest.
 

This is a very common question, and TCM (Traditional Chinese Medicine) practitioners always are educating the public about the scope of our practice.  There's a simple answer; we'll treat any problem you would see your primary care provider for.  Most people come in when they haven't been able to find out what's causing their health concern, or quite often, are tired of taking a once-a-day pill that never stops.  I say that I have a general practice and have a special interest in Women's health issues, migraine headaches, and arthritis (including rheumatoid, osteo, psoriatic, etc.)

Keep in mind that Traditional Chinese Medicine (acupuncture and herbs for example) has a 2,500 year written history… and it's still being practiced!  Think about all the conditions you would see in 2,500 years in a continuous society that had been ravished by war and plagues… just about everything. It's not the end-all-be-all medicine - nothing is.. or can be.  One of the greatest assets of this medicine is it's ability to treat a deeper root of disease, which Western medicine does not. Given patience and willingness to follow the advice of your practitioner, acupuncture and herbal medicine can work for a great variety of things.

For example, a medical doctor may treat a common cold by giving you a prescription for an antibiotic.. even if the cold is caused by a virus. Antibiotics kill bacteria, not a virus. Anyways.. the bacteria that Western medicine considers is the cause of the illness are often NORMALLY present in our bodies, and a virus can come and go and be dealt with by our immune system. Why would bacteria or virus cause a problem then? Usually, the immune system gets weakened and the virus or bacteria get out of control. So - what's the cause of the cold? The pathogen (virus / bacteria) or the weakened immune system? Our medicine would consider the weakened immune system to be the root cause. Therefore, I'll often treat the immune system to prevent you from getting sick in the first place.. and if you do get sick, I use various techniques to clear out the pathogen and then strengthen your immune system. I may also suggest lifestyle changes as well, since you also have to consider why the immune system was weakened in the first place - often due to poor diet, overwork, too much stress, not enough sleep, etc.. I think this whole story illustrates why western and Chinese medicine can be used together for great results. Sometimes with very strong pathogens, people can't come in frequently enough for treatments to be effective enough, so they will get some western treatment as well. Then in the recovery stage, I can strengthen the body to get back to a healthy state which prevents illness from coming back in.

Acupuncture.com has a sampling of what Chinese medicine is often used for. The National Institutes of Health has more of a western point-of-view on information about acupuncture.