Mentalization is the ability to understand your own and others behaviour on the basis of mental states. Mental states can be feelings, thoughts, needs, goals and reasons. We all mentalize when we interact with each other but we are rarely aware of it.
Mentaliztion is usually an automatic process that we aren’t aware of. For example when the interaction is going easy and we are feeling good with each other. We aren’t conscious about it but we are constantly aware of our own and other’s mental states and we adjust our behaviour accordingly. It can be small changes in like facial expressions or the way we say things. Automatic mentalization release mental capacity to other things.