"He is really shy."
Translation:Il est vraiment timide.
In French, the adjective "timide" (shy) is always written the same way (with an "e") in the masculine singular (il est timide = he is shy) or in the feminine singular (elle est timide = she is shy). We add an "s" in the plural (nous sommes timides = we are shy).
The full explanation is quite long to give. Instead, look at this link which explains very well how to use "c'est" or "il/elle est".