"He is a singer."
Translation:Il est chanteur.
But the translation here is "C'est un chanteur". I thought you use 'un/e' with professions only if they are modified by an adjective. E.g. "C'est un bon chanteur"
You may say either "il est chanteur" or "c'est un chanteur". The point is that when "est" is followed by any modified noun (un/une/le/la/l'), you should use "c'est".
As a general rule, you can't use "il est" with "un". In that case, you have to change the "il est" to "c'est".
Thanks! That answers exactely my question what's the difference between il est and c'est.
Please take a good look at this: http://www.frenchtoday.com/blog/cest-versus-il-elle-est