Omega-3 fatty acids are essential fatty acids, necessary for the human health. However, the body cannot synthesize them. Therefore,  we have to provide them from the diet.

Omega 3 fatty acids have so many health benefits:

Also known as Polyunsaturated fatty acids (PUFAs), they play a role in brain function, normal growth and development. They reduce the risk of heart disease.  The American Heart Association (AHA) recommends people to eat fatty fish at least twice a week. Research also show that omega 3 FA reduce the risk of inflammation and have a protective role against many chronic diseases such as heart disease, cancer and arthritis. Since they are concentrated in the brain, they are important for cognitive (memory and performance) as well as for behavioral functions.

Omega-3 to omega-6 ratio: 

The diet on which human beings evolved had a much lower ratio of omega-6:omega-3 compared to today’s diets.
Excessive amounts of omega-6 fatty acids and a very high omega-6/omega-3 ratio increase the risk of many disease including cardiovascular disease, cancer, and inflammatory and autoimmune diseases. Whereas, an increased level of omega-3 fatty acids suppressed the latter effects. It is very important to have the proper omega-3 to omega-6 ratio in the diet. Omega-3 fatty acids help to reduce inflammation. However, Omega-6, another essential fatty acid, is pro-inflammatory.
Therefore, you need to make sure that the diet provides the proper ratio to protect the body against inflammation. The Mediterranean diet, which emphasizes foods rich in omega-3 has a healthy balance between the 2 fatty acids. Many studies have shown that many people following this diet are less likely to develop heart disease.

Since many other factors are involved, the optimal ratio may vary with the disease.
Therefore, a lower omega-6/omega-3 ratio is more desirable in reducing the risk of many of the chronic diseases. We should aim to a ratio not higher than 4:1. 

Dietary sources of Omega-3 Fatty Acids: 

Fish, plants and nut oils are the primary sources of omega-3 FA. 

According to University of Maryland Medical Center, The omega-3 fatty acids have 2 sources, an animal source (EPA and DHA) and a plant source (ALA) . The animal sources include cold-water fish such as salmon, mackerel, halibut, sardines, tuna, and herring.
The plant sources include flax seeds, flax-seed oil, canola (rapeseed) oil, soybeans, soybean oil, pumpkin seeds, pumpkin seed oil, walnuts, and walnut oil.
The health effects of omega-3 fatty acids come mostly from EPA and DHA. ALA from flax and other vegetarian sources needs to be converted in the body to EPA and DHA. However, many people’s bodies do not make these conversions very effectively. This remains an ongoing debate in the nutrition community; fish and sea vegetable sources of EPA and DHA versus vegetarian sources of ALA. Other sources of omega-3 fatty acids include sea life such as krill and algae.

Precautions: 

As mentioned above, there are so many dietary sources of omega-3. If you want to take a supplement, you should always consult your doctor or knowledgeable health care provider. Dietary supplements have a potential of side effects and may have an interaction with certain medications. 
Remember to take the right amounts of essential fatty acids for best health benefits.