The first week at a new job is like drinking from a fire hose. There's so much new information, you can only hope to retain some of it.
That's completely normal!
I started a new job this week, and I'm not remembering everything I've been told. That would be superhuman.
Instead, what I'm focusing on is integration. How do the things I'm learning fit together? What's the big picture?
I can always ask questions or go searching for answers about the little details. But if I miss the forest for the trees, that'll take me much longer to fix.