Je dis au revoir à Paul.

Because dis is the je form of the verb dire in the present tense.

Present tense of dire:

• je dis = I say
• tu dis = you say
• il/elle/on dit = he/she/one says
• nous disons = we say
• vous dites = you say
• ils/elles disent = they say

So Je dis au revoir à Paul means I say goodbye to Paul.

French often uses dire with set expressions like:

• dire bonjour à quelqu’un = to say hello to someone
• dire merci à quelqu’un = to say thank you to someone
• dire au revoir à quelqu’un = to say goodbye to someone

So the structure is very normal in French:

• Je dis au revoir à Paul = I say goodbye to Paul

Because with dire au revoir, the person you are speaking to is introduced with à.

So:

• dire au revoir à quelqu’un = to say goodbye to someone

In this sentence:

• à Paul = to Paul

This is similar to:

• Je dis bonjour à Marie = I say hello to Marie

Au revoir is a fixed expression meaning goodbye.

Literally, it comes from an older idea like until seeing again, but you should learn it as one whole expression: au revoir.

So in this sentence, don’t try to translate it word by word. Just understand:

• dire au revoir à Paul = to say goodbye to Paul

Because au revoir is the full expression. It is not just the verb revoir.

The word au is a contraction of à + le, but in au revoir, the whole phrase functions as a fixed expression meaning goodbye.

So learners should usually memorize au revoir as one unit.

The most standard and natural order is:

Je dis au revoir à Paul.

You may sometimes hear or see:

• Je dis à Paul au revoir

but for most learners, Je dis au revoir à Paul is the safer and more natural pattern to use.

A good model is:

• Je dis bonjour à Paul
• Je dis merci à Paul
• Je dis au revoir à Paul

A simple approximate pronunciation is:

zhuh dee oh ruh-vwar ah Pol

A few helpful points:

• Je sounds like zhuh
• dis sounds like dee
• au revoir sounds roughly like oh ruh-vwar
• Paul sounds like Pol

Also, in normal speech, dis au connects smoothly, so it may sound a bit like dee-zoh because of liaison.

Yes, it is grammatical and natural, especially if you are describing an action:

• Je dis au revoir à Paul, puis je pars. = I say goodbye to Paul, then I leave.

But if you are directly speaking to Paul, you would usually just say:

• Au revoir, Paul.

So:

• Je dis au revoir à Paul = talking about the action
• Au revoir, Paul = actually saying goodbye to him

Yes. Since Paul comes after à, you can replace it with an indirect object pronoun.

So:

• Je dis au revoir à Paul
  becomes
• Je lui dis au revoir

Here:

• lui = to him / to her

Examples:

• Je lui dis bonjour. = I say hello to him/her.
• Je lui dis merci. = I say thank you to him/her.
• Je lui dis au revoir. = I say goodbye to him/her.

Au revoir is neutral and very common. It works in both polite and everyday situations.

Depending on the situation, French also uses other goodbyes:

• Salut = hi / bye, informal
• À bientôt = see you soon
• À demain = see you tomorrow
• Adieu = farewell, much stronger and less common in ordinary conversation

So au revoir is a very safe and useful choice.