First don't let it control your life!I let cause i was the fat stinking kid in high school.As for knowing set a goal say you wear a size 36 go buy a pair of 34's and set a date to fit in them.I use to weigh 250lb and out of shape almost my whole life 4yrs ago i was 240at i say 25+%bf as of today im 180lb and 11.2% i got here by trail&error doing it on my own.I learned over time it comes down to first your diet then how you train ,i just got done recovering from overtraining its not fun so plan training smart diet right (whole grains,lean meat,healthy fats,)set up a cardio plan (to lose the fat)and a lifting routine to keep and build muscle.Dont look in the mirror all the time you won't be able to tell ,do it once a week wear a belt and go by feel loose good tight time for more cardio or less food!