I love how easy it was to learn coding concepts by completing exercises in each lesson. The interface feels very clean and intuitive. Some exercises can be quite difficult if you don't know what exactly you're looking for. For example, some programming languages are not available as options within certain lessons, so you have to go back to previous levels before eventually being able to complete an exercise using those features. It's a great way to get started learning about different topics such as data structures or algorithms without having to read through hundreds of pages! The practice tests help reinforce what we've learned from the tutorial videos. The ability to create custom courses makes Codility extremely flexible when designing training programs tailored to your needs.