Translation:Halò a charaid!
It's in the notes for phrases under Vocative case.
The vocative case is used when you are speaking directly to someone and is to show that you are speaking to them and not about them.
If you are speaking to someone you use the "little a" and lenite (what the added h in charaid is called) their name. Masculine names also slendarise (get either an i or an e added to the end). I'm making it sound way more complicated than it is.
Ciamar a tha Seumas - how is James? (speaking about someone called James, no vocative case needed). Ciamar a tha thu a Sheumais? - how are you James? (speaking to someone called James = vocative case)