First day of IT apprenticeship - Advice?

What are you doing? Just use a ****load of jargon, C#, C++, DBMS, backend, MOSFET, binary, useless rubbish like that. Tell me what your apprenticeship is about and I'll give you a great list of useless but relative words to impress them with.

Ill be doing advanced web development, iOS mobile dev, databases and more but they are the main things. Its a Software Engineering course.

Oh cool, alright then for web development (I'm talking in terms of sounding as smart as possible, here), you're going to want to know the difference between frontend and backend, you should know the basics of PHP (or at least sound like you do), and understand how a server processes PHP. You'll definitely need to know a lot about SQL, since you're doing both web dev and database engineering, although I presume you already do since you're doing into such a specific apprenticeship. If not, just understand that SQL is a language which allows you to make queries to a database to get and set the information in it. PHP lets you manipulate the data. CSS (cascading style sheets) are classes which make a webpage look nice. Nobody uses HTML any more (I mean, they do, but it just doesn't look as good), so make sure you refer to CSS when designing webpage layouts.

You'll need to know about hacking, I guess, since you'll want to know how to prevent it. Sanitising code stops XSS (cross-site scripting). Making static (i.e. non-dynamic) parameters helps to prevent OWASP injection (PHP, SQL injection, etc.). Having a good server which can manage high traffic volumes prevents DDOS attacks.

iOs dev, I know very little about. I've done some android development but I spend the vast majority of my time building PC games for Steam. But most likely you'll need to know a lot about UI designing, using anchors to make sure that your app UI fits on any device and looks right, and other superficial stuff like that. You should also know about networking, and how you can link your app to online services (databases for scores, preventing hacking, leaderboards, etc.).

As I said, before someone comes along who thinks they're a ninja coder and wants to start correcting me, and telling me that I've missed stuff out, I was merely giving a very generic list of topic which could come up.