Adwords and Adsense are two sides of the same coin. Adsense is for publishers to monetize their content, and Adwords is for advertisers to place ads in on content providers websites.
If you want to make money with your blog, you will want to use Adsense for sure, but to “kick start” your growth you may want to also use Adwords to market your content.
It depends on your business, and yes Adwords will tell you how many people search for a given keyword each week, and? how much costs per click, and how many clicks to expect each week. A good SEM helps you optimize these. Depending on if you only do local business, you can also restrict your ads only to certain zip codes.
You have to comply with the rules of the Game, and respect their copyright. Mine Craft, not a problem, Rock? Band with music, Huge issue. It is always better if you can get permission of the game company before you post. That’s what I do on any of my stuff.