Yarn Weights and Hook Sizes [Crochet Basics]

I would love crochet or knight a beautiful light weight dress. How do I choose niddles and tread please..

Hey, will the project be ruined if i use a slighter smaller hook? Example. I have size 4 yarn, but the pattern calls for a 4.5 mm hook.
Will using this 4.5m hook instead of a 5.0 mm hook ruin my work?

In Germany we don't go for yarn size

Hi

Thank you ma'am.

Hard to actually see the yarns well with the white background.