Brain wallet = human memory.
Think about something (easy to remember but hard to predict which has to be meaningless)
For instance: "alice gone to barber shop to drink coffee"
Then use this page; https://brainwallet.org/#generator (You can download it and use it offline, it's coded in JS so it works client side).
For our example our public address is: 19JKY4xxx8hveoXp6nucHPQ6ayu2EqtAVY and it's  WIF priv key is: 5KF4m3tGeV5BfQFFmm7RUzmcgmAMA5WW23Bru22J98rSgfNrZFM

Ps: do not use known catchphrases like "to be or not to be" https://blockchain.info/address/1J3m4nneGFppRjx6qv92qyz7EsMVdLfr8R