Fasting in Islam is called Sawm, and it is one of the five pillars of Islam. It is obligatory during the month of Ramadan, which is the ninth month of the Islamic lunar calendar. It is worth noting that you should not say "Ramadan" alone  you should say "the month of Ramadan" or "Shahr Ramadan" in Arabic, because Ramadan is one of the names of God, so referring to the month by that name alone without saying "month of" is considered improper.

The fast begins at Fajr, meaning the moment the first light of dawn appears, and it ends at Maghrib. According to Shia Islam and the rulings of Sayed Sistani, Maghrib time does not enter the moment the sun disappears below the horizon. You must wait until the redness in the eastern sky; not the western sky; has passed overhead and begun to disappear. This means the sky above you and toward the east should no longer have that reddish glow. This is the sign that Maghrib has truly entered and your fast is over. This is an important distinction from how some others determine Maghrib, so make sure you are waiting for that eastern redness to fade and not just the sunset itself.

If you want an easy way to track prayer times, the direction of Qibla, and when exactly Maghrib enters according to Shia jurisprudence, a great app to use is Shia+. It will give you accurate prayer times based on your location and the rulings of the marjas, so you do not have to calculate anything yourself. If you prefer not to use an app and want to determine the direction yourself, you can use a compass. The Qibla direction from most of North America is to the northeast. You can also look up your specific Qibla direction based on your city and then use a compass to face that direction for prayer.

Fajr and Maghrib are two of the five daily prayers in Islam, and their prayer times are also the markers for when your fast begins and ends. So when the time for Fajr prayer enters, your fast has begun, and when Maghrib enters after that eastern redness fades, your fast is over.

During the fast you must abstain from eating, drinking, smoking, and sexual relations. This means no food, no water, no gum, nothing enters your body intentionally from the time Fajr enters until Maghrib.

Before Fajr, it is recommended to eat a meal to sustain yourself throughout the day. This pre dawn meal is called Suhoor. It is not obligatory, meaning you are not sinning if you skip it, but it is highly recommended because the Prophet did it and it helps you physically get through the fast. You can eat anything halal for Suhoor, and you must stop eating and drinking at Imsak, which is a buffer zone of around 10 to 15 minutes before Fajr actually enters. Imsak is not when the fast officially begins; the fast begins at Fajr, but Imsak is a precautionary margin so that you do not accidentally eat into Fajr time. If you eat right up until Fajr and stop the moment it enters, your fast is still valid, but treating Imsak as your personal stop time is the safer and recommended approach. The Shia+ app will show you both the Imsak time and the Fajr time separately so you can see exactly how many minutes apart they are for your location on that day. The practical advice for a new Muslim is to finish your Suhoor, stop eating and drinking at Imsak, and then prepare yourself for Fajr prayer so that your fast begins with complete certainty.

When Maghrib time enters and the fast ends, you break your fast with a meal called Iftar. It is highly recommended to break your fast with dates and water first before eating anything else, as this is what the Prophet did. After that you can eat normally.

Now regarding the intention — the intention is made in the heart, not the tongue. You do not say anything out loud. What you are doing internally is orienting your will toward the act, meaning you are consciously deciding that you are going to fast for the sake of God. It does not need to be a specific sentence you recite in your head, it just needs to be a genuine conscious decision.

A common question new Muslims ask is whether they need to make the intention every single night before each fast. The answer is no. You can make the intention once at the very beginning of the month of Ramadan, before Fajr of the first day, and intend to fast the entire month for God. According to Sayed Sistani this is sufficient and you do not need to renew it every night.

If it helps you to consciously think it through, you can say in your heart something like "I intend to fast the entire month of Ramadan for the sake of God alone," and that is perfectly valid and in fact encouraged because it makes the intention more deliberate and conscious.

The key principle is that the intention must be present before Fajr. If Fajr begins and you have not yet decided whether you are fasting or not, your fast for that day is invalid. So the intention must always precede the beginning of the fast.

Another common question is what time exactly should I make the intention. The answer is anytime before Fajr of the first day of the month of Ramadan. You could make it right after Isha prayer the night before the first fast, or right before you sleep, or right before Fajr enters — all of that is fine as long as it is before Fajr begins.

If you travel and your fast becomes invalid for that day, or you miss a day due to illness, your overall intention for the month is not broken. Those days simply get made up later after the month of Ramadan ends, and this makeup is called Qada.

Fasting is not only about abstaining from food and drink; it is also about guarding your tongue, your eyes, and your actions. Backbiting, lying, and arguing are all things that diminish the reward of your fast even if they do not technically invalidate it. As a new Muslim, think of the fast as a full body and soul experience, not just a physical one.

What actually invalidates the fast according to Sayed Sistani is intentionally eating or drinking, intentionally causing yourself to vomit, intentionally submerging your entire head in water, intentionally inhaling thick smoke or dust, and sexual relations. The word intentionally is very important here  if any of these happen by accident or forgetfulness, your fast remains valid. For example if you forget you are fasting and take a sip of water, your fast is still valid.

Those who are exempt from fasting include the elderly who cannot bear it, the severely ill, travelers under certain conditions, pregnant or breastfeeding women if fasting harms them or the child, and women who are menstruating. Most of these people must make up the missed days later except for the elderly if they are permanently unable.

Fasting is an act of worship done purely for God, and it is said that the reward for fasting is unlike any other act of worship because God himself said he will reward it directly.