There are many excellent online resources for learning about and solving equations.
WolframAlpha is excellent for checking solutions to equations; just type your equation into WolframAlpha.
(Note that step-by-step solutions are for pro subscribers, but you can get answers to as many equations as you want, so WolframAlpha is great for checking work).
Mathisfun has this very clear and easy to use interactive illustrating the solution of linear equations.
Also from Mathisfun we have a Quadratic Equation Solver, simply enter the coefficients (a, b and c) and the solutions and a graph will be returned.
Try this calculator from Math Warehouse, which clearly shows the working using the formula.
Centre for Innovation in Mathematics Teaching
CIMT have tutorials on equations: Linear Equations 1, Linear Equations 2, and Linear Equations with Brackets in their Interactive Resources