All you have to do is go to https://freecodecamp.org and click on the Map linkat the top right which looks like:
Once you click on the Map link, you will see a page like the following with topics and challenge links on the right side of the page. Just click on the first one under HTML5 and CSS called Learn How freeCodeCamp Works. You will need to read each challenge and follow the instructions which will tell you what you must do to get to the next challenge. You can always use the Map linkto go back to a previous challenge to review what you did or skip to another challenge you want to try.
When you get stuck on a challenge, most challenges have a Ask for help on the forum button where you can type a specific question you need help with related to the challenge.