Use the FOIL method to remember which components you need to multiply together. F= First two, O= Outside two, I= Inside two, L= Last two. Then add your answers together and collect like terms to simplify.
In this case, multiplying the First two components together (x and x) gives x2. Mulitplying the Outisde two components together (x and 3) gives 3x. Multiplying the Inside two components together (2 and x) gives 2x and multiplying the Last two components together (2 and 3) gives 6. Adding all this together gives x2+3x+2x+6. 3x and 2x can be added together to give 5x so this simplifies to x2+5x+6 which is the answer.