For keyword research, there are too many ways to research manually. you can use paid and free SEO tools or you can search by google search.
some SEO tools are listed here.
- SEM rush
- Moz keyword explorer
- keyword everywhere
- Google search console
- Google analytics
- Google Adwords
or in second way you can do keyword research by google auto search, when you type any keyword on google search then click on the search cloume, you will see there so many keywords created to the query.