This character is a Other Letter and is mainly used in the Arabic script.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it is written as Arabic letter from right to left. When changing direction it is not mirrored. The word that U+0631 forms with similar adjacent characters prevents a line break inside it. The glyph can be confused with 33 other glyphs.
The Wikipedia has the following information about this codepoint:
Resh is the twentieth letter of the Semitic abjads, including Phoenician rēš 𐤓, Hebrew rēš ר, Aramaic rēš 𐡓, Syriac rēš ܪ, and Arabic rāʾ ر. Its sound value is one of a number of rhotic consonants: usually [r] or [ɾ], but also [ʁ] or [ʀ] in Hebrew and North Mesopotamian Arabic.
In most Semitic alphabets, the letter resh (and its equivalents) is quite similar to the letter dalet (and its equivalents). In the Syriac alphabet, the letters became so similar that now they are only distinguished by a dot: resh has a dot above the letter, and the otherwise identical dalet has a dot below the letter. In the Arabic alphabet, rāʼ has a longer tail than dāl. In the Aramaic and Hebrew square alphabet, resh is a rounded single stroke while dalet is a right-angle of two strokes. The similarity led to the variant spellings of the name Nebuchadnezzar and Nebuchadrezzar.
The Phoenician letter gave rise to the Greek rho (Ρ/ρ), Etruscan , Latin R, and Cyrillic Р.