To do SEO, the first step is to look out for the keyword. Keyword research can be done by many ways. In modern days we have many tools like Google keyword planner, Semrush,Ahref, soolve and more to do the reaserch easily. While working on the Keyword research it is important to look out the search volume for a keyword,Keyword density, keyword gap in the market etc.
The Seed keyword is the main thing that talks about the business. Pillar keyword are the keywords that needs to be worked around the seed keyword.
Keyword research helps in bring relevant target audience to the website. Based on the search intent keyword search can be Navigational,Informational,commercial and Transactional
One simpe way to do the Keyword research is for example if we type on Google it gives auto suggestions. this itself says that there has been many searches happening on specific words. so we can start working on the keywords to rank better on SERP.
Consider the keyword density like how hard it is for a given keyword to get ranked. For this we need topical authority, Technical SEO, high quality useful content.