Here is an exemple of what i want to know: let's say I do a research on the word "game" and I find that people search on google the word "games" more offen. My quastion : It will affect my seo if i register a domain without the "s" from the end of the word? Another one: if are 3 words in the domain, how is better: with "-" or without?
Google is smart, it figures out your keywords without hyphens. As far as plural vs singular im not an expert, the topic has been discussed quite a lot: http://www.google.com/search?hl=en&q=SEO+plural+vs+singular happy reading and make your own judgments.
This is an interesting question. What I normally do is to determine whether a singular or plural term will sound logical with the contents of the site i'm looking at doing. I might be wrong. Insights from others will definitely be helpful.
My Friend internet business Success doesn't depend on the domain names. You keep your domain with "-" without it or with three words or more than that... It Doesn't matter at all... Learn all the skills required for the exposure of your website and be on the top of the search list...
Have both the domains with "-" and without and use one for branding and other for link building / and anchor text.