Whenever anyone uses search engine like Google, yahoo, msn or bing most visitors search top pages say till first 5 and they hardly ever go beyond that.

Role of Search Engine:
search engine use algorithm and by algorithm search engine decides the position of keywords, in SEO process two important factor are their ON PAGE & OFF PAGE OPTIMIZATION both are required for optimization .The onsite optimization revolve around altering textual and "meta data" to improve and imitate the relevancy of key words your are targeting for. This make sure that your website relevant face is put in front of the search engine, once the onsite activity is done most of the work carried out is offsite activity. The search engine looks in to the number of links directing to your website which establish the influence, conviction and relevancy.

Why SEO is required?
SEO is process which brings you on page 1 and if you are not at top position and your competitor is that means his website will have a good traffic, and traffic means would be client so if you want to be on page Top then SEO is must.