You can find the dedicated tutorials for Construct 3 on the website.
You can check out also its online manual out and the How do I FAQ topic which lists examples of implementation and answers to the usage of Construct 3 from our forums.
Be sure to check the general Learn section of our website.
You can also, when executing Construct 3, find bundled examples in the editor, from the start page.
In the left column you can select from full game demos up to advanced demos and tech examples.
You can also make use of the templates provided to kickstart your new projects.
For Construct 2, you can find dedicated tutorials on our website.
Otherwise, we have a free video playlist named C2 academy, providing with quite a few examples of use of Construct 2.
There is also the How do I FAQ (those examples can be used with Construct 3 as well, so checking out this massive thread is still relevant).
In addition to the tutorials and our online manual, we think this is the required documentation to learn how to use Construct 2 and Construct 3.
Construct 2 provides bundle examples as well in the "Examples" folder of where you installed it.
Moreover you also have access to templates when creating a new project.
The existing documentation for C2 applies to C3.
Learning how to use C2 IS learning C3.