Bonjour vs. bonne journée
While bonjour and bonne journée both relate to the idea of a good day, their usage is completely different based on timing. One is a greeting used upon arrival, and the other is a farewell used upon departure.
Bonjour
A1This is a standard greeting used when you meet or see someone for the first time during the day. It functions exactly like hello, good morning, or good afternoon.
Bonjour, je voudrais une baguette s'il vous plaît.
(Hello, I would like a baguette please.)
En arrivant au bureau, il dit bonjour à tous ses collègues.
(Upon arriving at the office, he says hello to all his colleagues.)
Bonjour Madame, comment allez-vous aujourd'hui ?
(Good morning Madam, how are you today?)
Bonjour ! C'est un plaisir de vous rencontrer.
(Hello! It is a pleasure to meet you.)
Quand on entre dans un magasin en France, on dit toujours bonjour.
(When you enter a store in France, you always say hello.)
Bonne journée
A1This is a parting phrase used when you are leaving someone. It is a way of wishing them well for the rest of the day and directly translates to have a good day.
Merci pour votre aide, au revoir et bonne journée !
(Thank you for your help, goodbye and have a good day!)
Je pars maintenant, passe une bonne journée.
(I'm leaving now, have a good day.)
Après avoir payé, la caissière m'a dit : bonne journée.
(After I paid, the cashier told me: have a good day.)
À ce soir ! Et bonne journée au travail.
(See you tonight! And have a good day at work.)
La conversation est terminée, je vous souhaite une bonne journée.
(The conversation is over, I wish you a good day.)
Summary
The essential difference is simple: bonjour is for arriving and greeting (Hello), while bonne journée is for leaving and saying farewell (Have a good day). You start an interaction with bonjour and end it with bonne journée.