Fard are those actions ordered by Almighty Allah and are compulsory. Anyone who rejects or denies a Fard becomes out of the fold of Islam. If a person leaves out a Fard without a valid excuse, then that person is a “Faasiq-e-Kabeer” or a great sinner. For example, a person becomes a great sinner by leaving out the Fard Salaah or not fasting in the Month of Ramadaan.
Fard-e-Kifaayah are those actions which are compulsory, but if they are performed by a few or a single Muslim, it ends the responsibility of other Muslims. For example, attending the Salaatul Janazah and burial of the dead by a few Muslims removes the responsibility from other Muslims.
Waajib actions are those actions which are second to Fard. If a person leaves out a Waajib action then that person commits a great sin. If a person rejects a Waajib action, he or she does not become a Kaafir. For example, if a person leaves out the Eid Salaah, Qurbaani or Sadqa-e-Fitr he or she does not become a Kaafir but is committing a great sin.
Sunnah are those actions which have been performed by Sayyiduna Rasulullah (sallal laahu alaihi wasallam). We should also try to follow these actions to get Thawaab.
Sunnat-e-Mu’akkidah are those actions which have been performed by Sayyiduna Rasulullah (sallal laahu alaihi wasallam) regularly without a break. A person must perform these actions regularly for, by neglecting these actions, he or she becomes a sinner. For example, performing the two Sunnah of Fajar, or Taraweeh Salaah or using the Miswaak during Wudu are actions that must be done regularly without a break.
Sunnat-e-Ghair Mu’akkidah are those actions which were performed by Sayyiduna Rasulullah (sallal laahu alaihi wasallam) with occasional breaks. For example, the four Sunnah of Asar and Isha Salaah.
NAFIL OR MUSTAHAB:
Nafil or Mustahab are those actions which are approved by Shariah (Islamic Law). A person who performs these actions will receive Thawaab. If they are neglected then it would not make up a sin.
Haraam actions are those actions that are clearly forbidden by Almighty Allah. If a person rejects this prohibition, then he or she becomes a Kaafir. One who performs a Haraam act is a great sinner. For example, it is Haraam to gamble, drink alcohol and to eat pork.
Makrooh actions are those actions disliked by Shariah.
Makrooh-e-Tahreemi is an action that is close to Haraam and brings punishment to those who do it. It must be avoided.
Makrooh-e-Tanzeehi is such an action that if it is avoided brings Thawaab, but if the action is carried out then there is no punishment.