Intergrating with respect to time, you get that v = u + at. Knowing that velocity is just the rate of change of your position ds/dt = v, and sustituting the previous expression for v, you get ds/dt = u + at. Integrating this with respect to t again you get s = ut + 0.5at2. To gain the further three equations given on your formula sheet it is just a matter of substituting and rearranging these formulae.