new to (all (of)) this
Completely inexperienced in some activity, profession, way of life, etc. I'm sorry for being so awkward. This is the first time I've ever been on a date, so I'm new to all of this. They didn't tell me the job entailed accounting work, so I'm a little new to all this. It's his first day working construction, so cut him a little slack—he's new to this.
(a little) new to (all) this
an apologetic way of saying that one is experiencing something new or participating in something new. I'm sorry I'm slow. I'm a little new to all this. She's new to this. She needs practice.