A pyramid has 3 sides, just like how a triangle has 3 sides.
A pyramid is basically a 3-D triangle, so it will also have 3 sides.
The same thing would go for cubes - If a square has 4 sides, then a cube will too (If you don't count the top and bottom!)
A sphere, however, has no sides, just like a circle. Isn't it cool how flat shapes have as many sides as their 3-D versions?
SHAPES ARE AWESOME!!
↑ ↑ ↑ Hope this helps! :D