@Yamatoman-san: MiyaMiya-san asked for extra help, not for criticism.
@MiyaMiya-san:
The first time you meet someone on a particular day, especially if it is still morning, you say "ohayou (gozaimasu)." Adding the "gozaimasu" is more formal. "ohayou" is a form of hayai, which means early in this case.
If you meet someone in the middle of the day or afternoon, you say "konnichi wa." konnichi literally means this (kon) day (nichi).
If you meet someone in the evening, you say "konban wa." konban literally means this evening.
These are normal polite greetings; there are also less formal greetings.
Here are some casual phrases to say goodbye to someone you expect to see again:
ja, mata, ja mata, ja ne, mata ne
When it is late at night, you may say goodbye by saying "oyasumi (nasai)", which literally wishes the other person a good rest (yasumi).
Another goodbye word is sayo(u)nara, but this is also what you say when you say "farewell" (not expecting to see someone again), so it is not used quite as much on a daily basis.
Hope that helps.