Learning to draw step by step is a matter of learning to see shapes. All objects have shapes, but it does not mean it has to be a perfect shape such as a circle or a square. It means that objects are simply a combination of shapes. An example is an ice cream cone, the ice cream would be a circle and the cone would be a triangle. The same can be done with a bull's head.
Sketch a shape that is similar to a rounded triangle to represent the head. For example, draw a horizontal arched line with curved verticals lines coming down on both sides, similar to a triangle. Then create a horizontal line to connect the two vertical lines. The bottom horizontal line should be about half the size of the top horizontal line.
Create a horizontal arched line across the bottom of the shape to represent the nose area. Shade in two ovals on each side for the nostrils.
Create almond shapes for the eyes. Place the shapes close to the edge and shade in part of it for the pupil.
Create an arched line between the two eyes that connects to the top horizontal line to represent hair. Add some short strokes for the hair.
Create crescent shapes for the horns with one on each side of the head. Have the shapes curve toward each other.
Adjust the lines as necessary, and then reinforce the remaining lines by going back over them.