Even when you validate sites like facebook you get various number errors and warnings but i don’t think it really effects the ranking of the site ,but I am not sure .So can anyone clear up my confusion?
[font=calibri]Google doesn’t see itself as the W3C police – it wants to give users the pages that are most relevant and helpful for what they are looking for. Whether a page validates or not doesn’t generally have an impact on whether a page is relevant or helpful, and so it isn’t considered as a factor in Google’s algorithm. But … Google uses one HTML parser, and your visitors will use a variety of others. Any validation errors in your code might cause any one of these to get confused or throw a tantrum, and while most errors are pretty harmless, you don’t want to run the risk of Google trying to read/understand your page and failing because the code is such a mess. It’s always worth checking that your code validates, and fixing any errors that you can, because then you minimise the risk of something going wrong … and if you do subsequently find a problem on your page, it’s much easier to put it right if the validator isn’t spitting back a long list of 200 other trivial errors that are nothing to do with it!
But no, minor errors that don’t stop Googlebot from parsing your page won’t have any impact on your position in the search results.[/font]
It doesn’t really matter. Of course you can use validators, and if you find any huge issues it’s a good idea to fix them. If you’re just learning HTML the exercise might benefit you.
Nobody will tell you how Google algorithm works however I would say it matters to avoid errors in HTML. As somebody said above: Google looks at the content and want to give users most relevant pages. True but code, usability and how you page works also have some significance. Just to mention a bit old but i hope current news from Pierre Far working for Google read here .
If your page validates then it will work in more browsers than if it doesn’t validate.
This. Proper coding will validate and look decent on 99% of browsers, devices and screen sizes. Not including IE7. Screw IE7. =-)
Psh, kids these days. IE7? no problem.
Now IE5 for Mac, that was a problem… 
if your website is validated it means that your website content is more visible to the google bot, which means it can index your website more easily.
so that has an effect on seo in short a website not vlidated properly with all other factors being equaly will rank lower than a website that validates properly with all other factors being equal