keyword question

Hey guys. Im loving the message board so far. I think I've learned more about internet marketing in the past week than the past 3 months of studying it, just because of the massive amount of input you get here. I'm extremely excited about hitting my earning potential from this.

So, Im working on my SEO and keyword selection techniques this week and I have a small question that I haven't seen answered i guess because its probably a pretty newbie question, haha. Anyways, when it comes to keywords, I've read that you don't want more than 15-20 words for a meta keyword tag but I was wondering the exact definition of a keyword. Is "how to fix stuff" a single keyword or would it count as 4 words out of the 20?

Also, i've found some good keywords that won't really make sense in a sentence next to each other and am wondering how a pro implements them. Do you add the keyword in the title, header, content, etc as is or is it ok to add a word in between. For example, lets say my keyword is "buy shirt", would it be better to have a title like "10 best ways to buy shirt" or would it be better to make it gramatically correct "10 best ways to buy a shirt". In the actual article I would make complete sentences and choose the 2nd choice, but for the title and description of the page would it be wise to throw in these gramatical errors just because it willl rank better for SEO?

Thanks for all the help in advance. I'm so new to this its not funny. Trying to wrap my brain around everything haha.