Choosing Your Specialisation

I know there’s been tons if posts on this topic but I can’t find one answering my question.

Im a bit confused what specialisations are available to be chosen once you pass training. I know about the Commando, Sharp Shooter, Assault Engineer, etc… that you can choose after 2 years of service (from what I’ve heard), but I can’t find the list for any that are available to be chosen straight out of training.

Feel free to roast me as this question probably sounds stupid.