Hello Augustin (@LeftProductions)! Welcome to Webflow community
For create such Hero section with slider on background I would suggest next steps:
1) Create full screen section, give it position: relative
2) Add slider inside the section, give it position: absolute, aligning: full, height: 100%.
3) Add images and information to slides
4) Add div to section (which will hold logo and arrow/link for scrolling), make it position: absolute, aligning: full, height: 100% and z-index higher than slider
5) Add navbar to the section, give it position: absolute, aligning: bottom. Style it as you need.
For make effect when navbar stick to the top you will have to duplicate navbar, make it (copy) fixed position and display: none by default. Then create interaction for original navbar with scroll trigger, which will affect duplicated navbar and make it display: block.
Hope I was able to explain. Feel free to ask if you need more help.