Instructions
Equip and withdraw your preferred weapon. As a Brahmin has few health points, it is prudent to use your best melee weapons instead of wasting ammunition.
Approach the Brahmin and place it within the cross hairs of your weapon. Hold the aim button to keep the cross hairs steady.
Press the attack button to assault the Brahmin. Press the attack button repeatedly to inflict enough damage to kill the Brahmin.
Press the V.A.T.S. menu button to bring up your V.A.T.S. options. Select the Brahmin as your target and select which parts of the Brahmin to attack. Select multiple attack points to increase the spread of damage. Confirm your selection, and your character will automatically carry out your commands with a better chance of hitting and performing critical damage.