The Arabic calligraphy has 6 different styles, which are Thuluth, Deewani, Kufi, Naskh, Riqa and Taliq.
The Arabic alphabet has 28 letters.
22 letters have all four forms, which are Isolated, Initial, Medial and Final. These 22 letters can connect to the left and to the right.
6 letters have only two forms, which are Isolated and Final form. These 6 letters do not connect to the left.
Letters Alif, Daal, Thaa, Raa, Zayn and Waw are six letters, which do not connect to the left. The only forms of these letters are the Isolated form and Final form. The Initial form and Medial form for these letters do not exist.
For each letter that comes in a written word after Alif, Daal, Thaa, Raa, Zaayn and Waw, a writer has to use its Isolated form (in case, if that letter defines the end of the written word) or its Initial form (in case, if that letter is further on combined with another letter). Always leave some small empty space behind Alif, Daal, Thaa, Raa, Zaayn and Waw when continuing writing other letters of the word.