Greenhorn (noun)

1. A person who is new and inexperienced in a particular job or activity.
2. A newcomer in a particular place or area of activity.

Origin:

From middle english grenhorn, from old english grenhyrne, equivalent to green +‎ hyrne, literally meaning "green corner" (hyrne being used in the sense of "horn", perhaps by comparison to the shape of an animal"s horn in profile). the original sense was a young deer with new horns, later extended to "young or inexperienced person".

Examples:

1. The CEO took the greenhorn under his wing and showed him the ropes.
2. Although she was a greenhorn in the world of finance, she quickly adapted to the fast-paced environment.
3. Many greenhorns make mistakes when they first start a new job.
4. He was a greenhorn in the kitchen and struggled to make even the simplest of dishes.
5. As a greenhorn in the field of politics, she had a lot to learn.