When did your toddler start talking?

My son is going to be 18 months this week and he doesn't seem to be as verbal as other kids his age or a little older. I know each kid develops differently but he is my first and I do worry at times.
He does however know how to say dada sometimes an also mom. He says hi to his little brother occasionally too 'hi Jace' and ha started to say uh oh. He is really good on understanding when we ask him something such as if he wants to have a snack or some juice etc. he communicates at most by showing us what he wants by walking to the fridge or pointing but I just wanted to see if he is on track?

Any ideas of fun ways to start teaching him numbers and alphabets perhaps? Anyone used the flash card techniques?
What have you done to help your child begin speaking more?

Thanks!