Fasting has two integrals:
1- The intention in the heart every day. One intends in his heart, for example: "I intend to fast tomorrow to fulfill the obligation of fasting Ramadan this year, faithfully and seeking the reward from Allah.”
The time of the intention is from sunset until the Fajr prayer begins.
2- To abstain from anything that invalidates fasting, from the appearance of the true dawn to the sunset.
The invalidators of the fast are many. Among them:
1- Eating, even if as little as a sesame seed and drinking, even if one drop of water or medicine, while remembering that one is fasting.