Steering Wheel shaking in all speed, but decrease when breaking.
Since you provided no information at all about your vehicle and very minimal information about the problem, I’m going to assume that you know little about cars.
Don’t mess with this. Take it to a good local & independent front end shop and describe the problem. Many places will look it over for little to no $$. You could have a problem as simple as a bad tire or tire balance or as dangerous as a wheel bearing that is on its last legs.
You probably have a bad tire – most likely on one of the front wheels. Run your palm over the tread of the tires to see if you can feel an uneven spot. That will be a sign that tire is defective.
Alternately, run the car (I assume) by a tire shop. They can inspect the tires, the tire balance, and the radial runout of the tire/wheel combination.
Hope that helps.
Potentially serious and unsafe, possible simple and cheap to fix, but we will need more information to do any half way reliable guessing.
I would suggest very carefully and slowly drive to a local shop.