Ceann Shannon

Since your images are from the film Iron Man, I'll initially address that universe. In the film canon, Tony constructs a miniature Arc Reactor and implants it in his chest. This provides a fantastic power source for the armors he later builds. In the Mark 2 & 3 armors, Tony uses his Arc Reactor to power repulsors (a fictional technology that uses energy to generate thrust), which his suit contains on the palms and feet (per Wikipedia).