20 years the Solar and Heliospheric Observatory was launched to the L2 lagrange point which is a point between the Sun and the Earth were the gravity is balanced, actually it orbits around this point because it is an unstable point. Over this time it has help many scientists study the sun such as:
Helioseismology. The sun is not a solid object but a giant ball of plasma. Plasma is a gas that is made up of charged particles, both negatively and positively charge particles. Being a not a solid object there is no real set shape, so the the Sun wobbles and jiggles. With Soho you can measure the wobbles and jiggles, scientist have used these measurements to figure out what the interior of the sun looks like.
CMEs or corona mass ejections. The sun from time to time ejects large amount of plasma from the the outer layer called the corona. These chunks of plasma can damage the electronics on satellites and also have downed power lines, so it could disrupt or lives on many levels. With Soho we have been able to predict if and/or when the hit the Earth.