Keyword research is the starting point for all SEO campaigns. What you learn during this process affects all your other actions.
To optimize a particular page, you need to know what phrases your customers are using to look for what you have to offer.
Keyword research is the process of finding the phrases your customers use, to find companies like you in the search engines.
The best way to get data about keywords is from the Google Ads Keyword Planner- if you have access to it.
An important part of keyword research is using data to evaluate which phrases you should focus on. Google Trends is a good way to do this for free.