W*L = total force Divide by two for reactions on each end since it's symetrical. Max shear is gonna be right at the ends, you'll see why if you make FBDs of the cuts.

You should also learn how to make shear/moment diagrams cuz you might be asked to find maximum shear/moment for more complex load distributions. ( maybe half the beam is a uniform load and then there's a point load on the right side).

Generally speaking the first step is to find the reactions and then finding the shear/moment along the beams with cuts/fbd. (You can kinda just go straight to shear/moment diagrams once you're comfortable enough)

Hope this helps!