Omega 3 fatty acids are important for health. Good dietary sources of them, among others, include cold water oily fish, such as salmon, herring, mackerel, anchovies, and sardines.

An evidence-based health professional like a dietitian will be able to review your diet with you and (if indicated) suggest changes to it to ensure that your omega 3 fatty acid intake is adequate.

Buying pills from Hyman's or Weil's on-line "Shops" (or any of the many others out there) is not a good idea unless it is recommended by an evidence-based health professional.

The conjecture that "You brain is mainly made of such fats" is factually wrong. The brain (like all other organs) is a mixture of water, proteins, nucleic acids, carbohydrates and fats (more formally, lipids). The omega 3 fatty acid content of the brain is tiny on a mass basis.