There will always be things you don’t know and as you first set out on the PhD journey you’ll suffer from a lack of experience and expertise.
But the more enthusiastic you are, the easier it will be to navigate this inexperience. Remain enthusiastic in your reading and learning. If you don’t know something, find someone who does and ask them. If you’re confused, tell someone. Keep an eye out for opportunities to polish your research skills and sign up for them when they come along. Say yes to new responsibilities where possible and never let your inner critic tell you you’re not good/smart/competent enough.
What you lack in experience you can more than make up for in enthusiasm.
Good luck and have a great week!