New iPhone, almost half my storage already gone

So today I bought a new iPhone 7 because my SE was very old.

I transferred all my data over iCloud because it was easier, but I checked my storage and I’ve already used near enough half of it somehow.

I checked the storage and most of it is full of “System” files, which I can’t access.

One of the biggest problems on the SE was my storage space, and I have no idea what to do if I have the same problem again. I really don’t have the money to do anything too major, and I only just got the phone today so I’m a little worried.