Answer 1

OMG !! There are so many projects that you can try !! If you always think that everything is already made by someone else, you'll be never able to make anything bro ! Just try to make something new !!

Answer 2

You'll obviously forgot them unless you practice them 😉

Answer 3

You learned the basics, you can already create a simple website. It is now time for intermediate to advanced.
How to practice? Watch a bunch of videos that have projects such as building full websites.
I'll set you on the right path.
https://www.youtube.com/results?search_query=html+and+css+website+udemy
Take the first video that pops up.