Exoplanets, by definition, exist outside our solar system, orbiting other stars. That means they’re pretty far away. Telescopes, even top-notch ones like Hubble, can’t image anything as small as a planet outside our solar system. Even Neptune, in our own solar system, is a blurry blue ball when viewed from Earth’s orbit.
So planets outside our solar system are practically invisible. However, planets can and do affect their stars in measurable ways, and that’s how astronomers find them.
The two most widely used methods are transits – the blinking method – or Doppler shifting – the wobble method.