The title sounds vague, but just most of the topic in one pack :)
2x + 3 = 6 <-- This is a simple, linear equation. Easy to solve and to work with in general.
The number infront of 'x' is the x-coefficient. This just means x multiplied by the number. Anything we do to one side, we MUST do to the other side of the =. Always, when it changes the value. (So not when factorising or simplifying)
In this equation:
2x = 3 [-3 from both sides]
x = 1.5 [divide both sides by 2]
So that stuff is simple enough. Now for it to get a little more tricky...
Quadratic Equations:- Factorisation
If we're given an expression such as: x^2 + 3x + 2 [x^2 means x squared, in case you wondered] it can seem quite mammoth really. But it isn't that hard.
I'm sure by now that you have seen factorisation:
4x + 2
2(x + 1) <-- take a common factor out of the expression
So, given x^2 + 3x + 2, we know we have to try and factorise it.