BON VS BIEN
Bon is usually an adjective and can mean good, suitable, efficient etc. Examples include: ‘Il a bon coeur’ (‘He is kind-hearted’), and ‘J’ai passé une bonne soirée (‘I had a nice evening’). Bien can also be used as an adjective, but only with state-of-being verbs such as être. It translates as good, moral or right etc. An example is ‘Ce n’est pas bien de faire ça’, (‘It’s not nice to do that’).
Bien is usually an adverb and translates as good; it can also be used to stress something. Examples include ‘Mes parents vont bien, merci’ (‘My parents are well, thank you’) and ‘J’ai bien reçu ton message’ (‘I did indeed receive your message’).
Bon is also used as a noun, and can mean form, voucher, coupon etc. Examples include: ‘un bon de commande’ (‘order form’) and ‘un bon de réduction’ (‘coupon’).