もっと

もっと means "more": もっと食べてください, "please eat more"; もっと安いのはありますか, "do you have a cheaper one?", literally "a more cheap one".

Japanese adjectives have no -er form, so もっと is how you ask for a bigger, cheaper or quieter version of something. When the comparison is obvious, no より is needed.

With a verb, it's more of the action: もっと勉強したい, "I want to study more".

Don't mix it up with もう. もう一つ is "one more (item)"; もっと is "more" in degree or amount. もっと and 一番 are the two ends of Japanese comparison: more, and most.