The personality of most people is hard-wired. Knowing your own personality may help in understanding why you prefer to do things one way and not another or why you think one way and not another. Likewise, knowing how another person is wired can help you understand, relate to, or at least tolerate that person’s personality.
Such knowledge can be a great help to finding a career that best suits you. Enjoying what you do for a living means having a sense of purpose and meaning in the world which can lead to self-satisfaction. This recalls the proverb “Enjoy what you do for a living and you will never have to work a day in your life”.
Knowledge of your own personality and that of others can help in relationships as well, whether that is with your spouse, significant other, children, supervisor, subordinates, or co-workers.
The Myers-Briggs Type Indicator (MBTI), which stems from the work of psychologist Carl Jung, is perhaps the most well-known personality profiler. Enneagrams are another.
There are numerous web sites and books that describe the various models of human personality. Many of these sources provide self-tests (some are free and some charge a fee) to aid in identifying your own personality profile.
For a brief start on the MBTI, see the article “Find your ‘Millionaire Code,’ then your new career“. That article links to The Personality Page, which contains among other things a collection of fairly detailed descriptions of each of the 16 personality profiles. For information on Enneagrams, see The Enneagram Institute.
Please note that I have no formal connection to any of the organizations linked here and cannot vouch for their accuracy, authenticity, credibility, or effectiveness. There may be better sources than these. But I have found their material useful for my personal purposes and this is the only reason I mention these particular sites. Good luck!