Since you are talking about simple harmonic motion the equation of motion will have the form:
You can take your pick between the two, but I will assume the first option.
1. If you substitute X=0 and y=10 into the equation then you can solve for A.
2. Velocity can be found by differentiating with respect to t. Now you can substitute t=0 and y'(0)=0 and solve for B (velocity at time = 0 is zero).
3. Substituting y=5 and the time at which this occurs will then allow you to solve for w.
4. At this point you have a complete equation of motion and can find the position at any time t.
5. Differentiating your equation for motion will give you the velocity at any time t.