You level up on Freecash by completing offers and surveys.
Each level requires you to earn 1000 coins so you'd reach level 20 after earning 20,000 coins.
When you hit level 20 you will have full access to the Freecash site. Until then you will only have access to Lite Mode.
https://faq.freecash.com/en/articles/9173633-lite-mode
Levels are granted permanently and there is no way to lose them.
Reaching level 100 grants you access to the VIP chat room.
Additionally, your daily bonus ladder rewards increase the higher your level gets, you can learn more about our rewards in general via the article below:
https://faq.freecash.com/en/articles/7748855-full-rewards-bonuses-guide