The common tiers run from full frame at roughly 36 by 24mm, through APS-C at around 23 by 15mm, Micro Four Thirds, 1-inch, and down to the small sensors in phones and compact cameras. The measurements describe area, and area is what determines how many photons the chip can collect.
Bigger sensors gather more total light at a given exposure, which generally means cleaner images at high ISO and more dynamic range. They also produce shallower depth of field for the same framing and aperture, which is much of why full-frame footage reads as cinematic.
Bigger is not automatically better. Large sensors demand larger, heavier, more expensive lenses and deliver less depth of field at a time when you may want more. Small sensors keep cameras genuinely pocketable and make deep focus easy — a sensible trade for a camera whose job is to be carried everywhere rather than to win a low-light test chart.