a – un (m) / une (f)
(Pronounced uh (m) or oon (f) (barely pronounce the n)
To remember that a is pronounced uhn (un/une) in French, use the following mnemonic:
The A acts like an umbrella (un) for the small creature, and with a balloon (une) attached, it can float away.

Examples of un/une (a) in a sentence
J'ai un frère.
(I have a brother.)
Il veut un vélo bleu.
(He wants a blue bike.)
J'ai une sœur.
(I have a sister.)