How do mixed language classes work?

I'm English speaking and have applied for a course to learn Dutch. The class is available to anyone speaking English, French, German, Spanish and Polish.

I'm really curious as to how these are run without everyone speaking the same language to begin and wondered if anyone had any
personal experience of such a class?

What is the best way to learn Polish?

I'm in high school and learning Spanish, but I REALLY would like to learn Polish (one day I hope to visit a friend who lives in Poland). For now I've just been printing out some basic Polish phrases and travel vocabulary. Does anyone have suggestions for the best way to learn Polish? Should I go to a class, buy a software program... etc. I'm not looking for a quick and easy way, I'd really like to learn the actual language, not just phrases.

It'd be awesome if your answers were from personal experience with the Polish language.