1) What is SEO?SEO stands for search engine optimization. It refers to techniques that help your website become more visible in organic search results for the people who are looking for your brand, product, or service via search engines like Google, Bing, and Yahoo
2) What's the difference between organic vs. paid results?Organic results are the results that appear in search engines, for free, based on an algorithm. Paid -- or inorganic -- search results appear at the top or side of a page. These are the links that advertisers pay to appear on different search engines.
4) Should I optimize my domain name to include keywords?Your primary domain should not include a keyword just for the sake of keyword optimization -- that can actually hurt your SEO. If your company name happens to have a keyword, that's fine, but don't go buying inboundmarketingsoftwarebloggingsocialseoemailautomation.com. Get what I mean?
5) How do I know when I’m using the right number of keywords on a page?Unfortunately, I can't tell you an exact number that is the "right" number of keywords on a page, mostly because that's the wrong way to think about keyword optimization.
There's no keyword density you should be aiming for -- in fact, using a keyword too many times can result in penalization due to "keyword stuffing." Just keep the reader in mind, and only use keywords when you need to. You'll find enough natural opportunities to include keywords that you won't even have to worry about reaching an arbitrary number.