Understanding what your keywords are is easier for someone and hard for others. Either way, keyword research is not something that should be rushed.
To find your keywords however you need to know first how people search. Once upon the majority of searchers typed in one-word keywords but eventually they were realizing if they put more words in the search window they will get more specific results. Studies also show that four-five word search terms have a higher ROI (Return on Investment). Basically, people who type in more words are more likely to buy. Not every searchers are there to buy. Many only are looking for only information.
However this makes building your website around keywords more difficult. You might have hundreds or thousands of keywords for your products and services.
Finding all the keywords is not difficult, there are many tools that you can use. One is the Google’s Keyword Tool which is free to use. Then there is the Wordtracker tool which is partially free. These are my favorites to use.
Brainstorm! Try to think how your customers think and start writing. Use core terms first then expand them to all variations you can think of. Use the tools I mentioned above, they will help you come up with more variations.