Sukoon (سكون) is a small circle (ـْـ) placed above an Arabic letter to indicate that the letter has no vowel following it — the consonant sound is produced and then stopped. For example, in the word مَسْجِد (masjid, "mosque"), the letter س carries a sukoon, meaning you pronounce the "s" sound without any vowel after it, going directly to the next letter. Sukoon can appear on any letter except at the very beginning of a word (Arabic words always begin with a voweled consonant).
Shaddah (شدّة) is a W-shaped mark (ـّـ) placed above a letter to indicate that the letter is doubled — it is pronounced twice in succession. The first instance is with a sukoon, and the second is with the vowel that the Shaddah letter carries. For example, عَلَّمَ (allama, "he taught") has a Shaddah on the ل, meaning it is pronounced as if there are two Laams: عَلْلَمَ. This doubling must be clearly articulated; skipping it is a Tajweed error.
Both Sukoon and Shaddah are extremely common in Arabic and the Quran. Understanding them is essential because they affect many Tajweed rules. For instance, a Noon or Meem with Shaddah must be held with a ghunnah for two counts. Sukoon on certain letters triggers Qalqalah (if the letter is one of the five Qalqalah letters). And many instances of Idghaam result in a Shaddah on the merged letter.
In our course, you will practice reading words with Sukoon and Shaddah from the very early lessons. Interactive exercises let you tap or click on the correct mark, identify words with Shaddah in Quranic verses, and practice reading aloud. By the time you complete the Simple Arabic program, reading Sukoon and Shaddah will be completely natural.