The first thing we normally say to start the conversation is saying greetings. We say ;hi, hello and the similar things to greet someone. In more formal situation people use 'good morning, afternoon, etc. Bahasa Indonesia has the same system. For friends, we use 'hai' or 'halo' but for more polite function we say depend on the time, in the morning we say "selamat pagi, in the afternoon we say 'selamat siang' and in the evening we use 'selamat malam'. Actually the word 'selamat' can be used for some occasions such as :
- selamat jalan for a leavetaking person
- selamat tinggal which means good bye
- selamat ulang tahun for happy birthday
- selamat natal for merry Xmas
So I guess you know the meaning of 'selamat tahun baru'....