Hammer Curls look a lot alike the basic dumbbell curls. It is no coincidence that it has the name Hammer attached to it because it simulates the same movement like when working with a hammer.
Like all the standing exercises done with dumbbells, stand straight with chest forward and knees slightly bend. Now, instead of moving the dumbbells horizontally towards your chest move them in a vertical position. Keep straight body posture throughout the exercise. Exhale when lifting the dumbbell, inhale when lowering the dumbbell. Make 3 sets with 12, 10 and 8 repetitions. Start with a normal weight dumbbell that suits you, and increase on every set by at least 3 kg per dumbbell.