You may (or may not) have noticed the link in the top navigation bar (^) between "Tutorials" and "Arcade". Manual
You may already have clicked on it, a while ago.
Be sure to click it again and read it.
It's now 100% complete.
For beginners (and even advanced users, always good to refresh its memory) it's an interesting read. Especially articles like "How events work" or the "System object references", "the interface", "saving and sharing projects" or yet "the best practices for C2".
You can read it from top to bottom or browse for a peculiar article.
It's really insightful on how Construct 2 works.
I would profit from this post to express all my thanks to Ashley and Tom for the writing and displaying of this manual. Another awesome effort of yours and be sure it is noticed and appreciated a great lot.
And now Read the fabulous manual! RTFM
You can also find the manual in eReading format thanks to Nikou and in PDF format thanks to NickyDude. Another PDF version by zsangerous.