Shadda

• A shadda sign that appears over a letter represents two of the same letter (double consonant), The first letter having sukoon and the second letter having its vowel.

• A letter having shadda must be pronounced twice. A letter with shadda is called mushaddad

•  Shadda does not appear at the beginning of a word, it is always written on top of the mushaddad letter, and the short vowel appears either on top or on the bottom of the shadda sign.

Examples from the quran