Keyword research is the life blood of Search Engine Optimization aka SEO.
Just adding keywords to the website without doing a keyword research is like sowing seeds in sterile land. The basic purchase of keyword research is to find out what keywords people are using to find your related products or services. Keywords suggestion tools render handy insights about the search behavior of people.
Tools like Google keyword suggestion tool, Word tracker, Keyword discovery etc. can list out keywords people are search for to reach the websites of you related products or services. Having those keywords in the web pages and executing the SEO techniques will increase targeted traffic to your website. High competition for the researched keywords would delay the keyword ranking process. Even then good SEOs can make your websites rank for high competition keywords by employing white hat SEO techniques in a systematic way.