Hello, I have a pain in the sole of my left foot only when I walk, on the other hand I don't feel any pain in my right foot. Thank you.

Differential. If the pain is on the back of the sole of your foot, it can numerous thinks. These are planar fascitis (usually worse when you get up and toward middle) or calcaneous fracture. In front, different set of problems. But there are other possibilities.
Plantar fascitiis. is what I would start with.