Single word describing a person new in something [closed]
novice:
a person who has just started learning or doing something
Novice is derived from the Latin word novus, which means new.
- A novice is new to what they do, so a novice photographer is just learning how to take nice pictures
(MW)
The obvious one is novice: "A person new to and inexperienced in a job or situation" (Oxford)
Neophyte is an alternative: "A person who is new to a subject or activity" (Oxford). To me that emphasises newness over inexperience, so it's a bit closer to what you're looking for - though it's quite an obscure word so I'd be cautious about using it.
But neither quite implies "for the first time". If it's important to stress that it literally is the first time, I'd just be explicit and say first-timer (or first-time participant, etc.)
If you want to highlight the 'first-timer' part...
a virgin.
- A person who is naive, innocent, or inexperienced in a particular context:
he’s a political virgin
[ODO]