Quantum physics properties, such as energy-position uncertainty, are unfamiliar to our experience. Strange as it may be, quantum physics accounts for observed atomic structure and behavior.
Nucleons (protons and neutrons) make up the core of the atom. In the solar-system model, the nucleus is the "sun."
Mass-energy conversion is relevant within the nucleus. Proton and neutron masses are slightly smaller when bound in a nucleus then when floating by themselves. As atoms form, the mass-converted-to-energy process is what keeps stars (and H-bombs) shining.
Imagine electrons as hazy "probability clouds" of various shapes. Finding an electron some distance from the nucleus is never a certainty in the way that finding a rock some distance from a slingshot is---the "cloud" title derives from this.
The "probability clouds" (orbitals) aren't scattered haphazardly around the nucleus. Orbital shapes depend on electron number and light absorption by the atom. Outermost orbitals form the (likewise hazy) boundary of an atom.