A brainwallet refers to the concept of storing a NEM in one's own mind by memorizing a mnemonic recovery seed. If the mnemonic is not recorded anywhere, the account can be thought of as being held only in the mind of the owner. If a brainwallet is forgotten or the person dies or is permanently incapacitated, the account is lost forever. Using techniques like memory pegging allow them to be memorized and recalled easily.
Fire up the Lightwallet and create a new account.
Your brainwallet should NOT be a simple password like 'password0' or even '*dsh89h8H&(hD31#$', the both can be bruteforced very easily, and the second one is hard to remember.
Instead, you should securely generate a seed, such as
witch collapse practice feed shame open despair creek road again ice least
and use that as your brainwallet password. It has been proven that a string of 30 words is very easy to remember, and hard for an attacker to guess.