Fantastic tool to make anyone comfortable with Salesforce. Are you new to Salesforce or searching for any topic in detail. Here you go.
Here you will find info specific to each topic and in detail. I would recommend all to go though this specially those who are thinking to give certification exams.
The only problem while registering is I was not able to associate my DE with trailhead because I've registered a namespace. So I created a new profile and completed some of the courses.
So steps are pretty simple
1) Go to this link
2) Select the module which you want to start with and then start your challenge.
Every time you complete a challenge you get points against it which is awesome. To get the points either you've to answer some questions which are related to the specific topic or you need to follow some instructions in your organisation.
Like recently two new modules have been added
Here explained all aspects of securing your data, like privacy of one's data from another. Or if records are visible to others they can't be edited. Or if can be edited then only few specific fields.
This excersise is super helpful for all those who are struggling with the sharing rules, permission sets etc..
Must read module specially for developers. This will help you better understand what you should follow while developing a functionality like first develop in sandbox, then deploy it to UAT/Testing org to make sure everything is working fine as generally UAT is full copy sandbox and exact replica of production. And then deploy it to production, this way you can ensure that your functionality is bulletproof and your production is safe to run on it.
These are just sample explanations, don't miss looking in all modules and many more are being added.