So, first, i am really sorry about my english. :-\
I was planning a Game like "Below the Root". It is a Jump n' Run Game with Adventure Game elements.
Can I make such a game and how?
Can I make such a game: yes.
And how: well...
It's perfectly possible to code a Jump'n'Run in AGS, but if you're new to AGS (or game programming in general) you might (will) be better off using an engine that's geared more towards Jump'n'Runs.
I'd try GameMaker; adding adventure elements to a GameMaker Jump'n'Run is much easier than adding a Jump'n'Run engine to an AGS adventure.
To make something like Below The Root in AGS, you have to code a TileEngine with collision detection and enemy AI. From scratch. Imagine building a car from scratch.
My point is, if you have to ask how to code a Jump'n'Run, you probably aren't supposed to code one in the first place. Might sound harsh but is true nonetheless :)
Or you could use PlaTENG (http://www.adventuregamestudio.co.uk/yabb/index.php?topic=40922.0). ;D
Right! I completely forgot about that. :-[