Omega-6 FA (fatty acids) are ubiquitous in the foods we eat and are not something you need to really focus on as far as supplementation of them. However, Omega-3 FA are found, as others have mentioned, in Flax Seed (oil is more concentrated form) or even better in the fat of fish (the best source).
0-6 and 0-3 FA's vie for position on the cellular membranes of cells with most being 0-6. Now, studies have shown (sorry do not have the specific literature as we speak) that if one ingests more 0-3 FA's they can and do replace the 0-6 FA's on the membrane. Why would one want to replace the 0-6 with 0-3? In Short, 0-6 FA's are pro-inflammatory and 0-3 are anti-inflammatory. Meaning, the derivatives of 0-3 actually act to decrease inflammation and the opposite is true for 0-6.
If you want to read some more information on them refer to this link:
http://ods.od.nih.gov/...cidsandHealth.asp#h3 To answer your ? about which one to buy, look for the one with the highest concentrations of EPA and DHA available.
ERIK
"Spectacular achievements are always preceded by spectacular preparation."