In modern Western numerology, your Life Path number comes from your birth date, added up and reduced to a single digit. The arithmetic is simple, and schools differ a little in how they do it, so your results always show each step.
A worked example
Birth date 14 July 1990, reducing month, day and year separately
Example date chosen for illustration. Adding all eight digits at once (1+4+0+7+1+9+9+0 = 31, then 4) gives the same result here, but the two orders can disagree for other dates, especially around master numbers.
Master numbers
Some schools stop at 11, 22 or 33 and call these master numbers. Others always reduce to a single digit. Your results always show which rule was used, so you can compare both.