First, collect all terms to the left side, and you are starting with x^2 - 3x - 10 = 0. Now you recognize that you have a quadratic equation. There are (at least) three ways you can solve quadratic equations: (1) through factoring, (2) completing-the-square; or (3) quadratic formula. For monic quadratics (i.e. quadratics that have a leading coefficient on the x^2 term of 1) it is smart to consider factoring, before moving to the quadratic formula. In this case, in order to factor, you need factors of -10 that sum to -3. These are -5 and 2. Thus x^2 - 3x - 10 = (x-5)(x+2) = 0, and the solutions are x=5 and x=-2.
If you need more help, please clarify where you are in the process and what's giving you trouble. I'd be more than happy to continue to assist.