A normal microscope uses normal light (visible spectrum) that bounces off the specimen under the microscope to create images. There are many types of waves that make up the electromagnetic spectrum. Visible light is just a small part of it. Other types include X-rays, gamma rays etc. Since visible light is not exactly from the ‘smallest wavelength’ part of the electromagnetic spectrum, the bounced wavelengths aren’t very small themselves and cannot produce images of small specimens.
Electron microscopes use beams of electrons, instead of normal light, to light up the specimen. Since electrons are way smaller than photons (visible light particles) they have a higher magnification power.
How is a scanning electron microscope different from a normal electron microscope?
Scanning Electron Microscope is a special type of electron microscope that doesn’t need light to reflect from its specimens. It instead uses the physical changes like heat, emission of electrons etc that arise from the irradiation of the specimen by the electron beam, to create images. Hence you can observe the enhanced magnification and detail in the above images of sugar and salt crystals. (Source)