A vow is an earnest promise or pledge that binds one to a specified act or mode of behavior. To take a vow means you make a promice to yourself to do certain things in certain ways. The vows help us discipline ourselves. The vows are very important to help reduce bad karmas and accumulate good karmas. There are various types of vows like chauvihar (not to eay and drink from sunset to sunrise or certain period of time), ektana (to eat for one time a day siutting in one place), upvas (not to eat for thirty-six hours starting from sunset day before till sunrise next day) , samayik (to sit in peace for forty minutes in one place without being affected by worldly thoughts or things). The different vows can be for different times. The sadhus and the sadhvis take five great vows, not to 1) do any violence (himsa), 2) lie, 3) steal, 4) be unchaste, and 5) be possessive. Thye take these vows for the rest of their lives.
The vows you take should be observed very carefully.