Rooms can fall into three main level of difficulty. You can distinguish them by the color of the bar present on the right corner of each room at the following link: https://tryhackme.com/hacktivities.
Green: Complete beginner to easy rooms; Yellow: Early intermediate to intermediate rooms; Red: Advanced and insane rooms.
Moreover, is important to note that you will find mostly two types of rooms: Walkthrough and CTF/challenging room. The first ones will guide you through an argument with explanations, examples and clarifications. The second ones are meant for you to test yourself and are designed with a hands-on approach.