The particle alif (أ), or more accurately the hamza, is used as an interrogative prefix or as a particle of equalization. Although the interrogative sense is used far more frequently (over 500 occurances) it is the rarer equalizational sense which is used first in the Quran, in verse (2:6) of sūrat l-baqarah:
Sahih International: Indeed, those who disbelieve - it is all the same for them whether you warn them or do not warn them - they will not believe.
The Interrogative alif Prefix
The prefixed alif is an interrogative particle (همزة استفهام) used to form a question and is usually translated as "is", "are", or "do". The dependency graph for verse (95:8) below shows an example of this use of the alif prefix. In general, both the particle hal (هل) and the alif may be used to form an interrogative sentence, although the prefixed alif is not usually used with with the definite article.
(of) the Judges?
(the) Most Just
Fig 1. An interrogative alif in verse (95:8).
The alif of Equalization
The prefixed alif of equalization (همزة التسوية) occurs six times in the Quran, with the first use of this particle at (2:6:6) shown below. This usage of the prefixed alif is not interrogative and instead indicates equality. This particle is usually translated as "whether".
whether you warn them
Fig 2. The alif of equalization in verse (2:6).