I’ll provide my usual advice.
First unless you are pretty good with code and systems administration, which it sounds like you are not, I would recommend sticking with 1.7.1 for now. Anything you learn and do in OH 1.7.1 will be transferable to OH 2 when it is released but given that OH 2 is alpha you might encounter problems with it that will be a challenge for you to solve on your own.
Download and install OH 1.7.1 (if on Linux use the apt-get method described on the wiki.
Download and install the demo from here and also get Designer installed and working.
Spend some time with the Demo and the wiki pages to get a feel for how OH works and how the major pieces work together (Items, Rules, Persistence, Bindings).
Also look for examples, particularly for rules. There are tons of examples on on the wiki (bottom right column) and in this forum. For example, here is a posting where I provided my weather config (NOTE: there are some typos in that posting, read below it for corrections).