How can I use the keywords for optimization?

Work on Meta Tags, write accurate title, description of the page and use the keyword in both (only the primary keyword as per that particular page perspective). Submit quality written articles and blogs with the keyword linking back to your site's relevant page. Make sure you do not write article/blog as if you are promoting yourself/site. Also make sure that you have not given much keyword in Meta tags, try to use less and relevant keywords. Make blog comments (only quality, relevant and instructive) with that keyword on dofollow blogs and forums only.

Why are you posting twice these things?

When you are going to start seo here is two main parts of seo. 1ST) On page seo. 2nd ) Off page optimization. both are very important.

There is a need of high searches and low competition for choosing keywords!!

Depends on what keywords you applied ....
Control with GoogleKeywordTool

Check Market Samurai. It is one of best keyword analysis tool and you will get more ideas from there also.

wow good information ......!!!

Hi..
When we are going to start for keyword optimization,first we look for its searches,how much competition is taking place on our targeted keyword,after this we have to care of much keyword in Meta tags, try to use less and relevant keywords. Make blog comments (only quality, relevant and instructive) with that keyword on do follow blogs and forums only.

You learn about marketing strategies only after experiencing it.