I'm starting my new job as a System engineer next week, is there any good advice? What should I expect?

Any good ideas are welcomed!

Congratulations!

80% of programming is reading code, not writing it! So read code and read a lot. It's an indispensable skill.

Congratulations. You'll have a great time by learning tons of new things. Don't get discouraged because there's too much to know. Just try to find a good mentor and go for it.

Ask for everything, do not feel bad if you miss something or if you don't know about some topic. Work with new teams could be challenging. And yes read a lot to understand the way of the project works

"System Engineer" is a very broad job-title. What you can expect will depend greatly on what your particular employer thinks "system engineer" means.