As said before, value bets are bets that you want people to call.
Obviously if you hold the nuts, you want a call.
However value bets are not just done with the nuts, they are done any time you feel you are ahead of the range of
hands he could hold, i.e. you beat him more times than he beats you.
This means that its fine to loose with a value bet so long as you are confident the range of hands you assign him is correct.
You need to value bet as often as is possible.
Often players don't value bet for fear that they are beat. If you base that decision on the number of hands in his range that beat you vs the number you beat that will call and it turns out he wins more often than you win, then its fine to check.
However if you are ahead of his calling range than you must bet because if he winning prior to the bet because you are building a bigger pot which you will win a higher percentage of the time. By not value betting when there is the opportunity to do so, you simply win a smaller pot a high percentage of the time.
Therefore in order to value bet, you must assign people calling ranges.