Hello, Hey, Good day or Hi! The greeting you use depends on who you are greeting and the situation you are in. Maybe you use Hey and Hi with people you know and in more informal situations and Hello with people you don't know very well and in more formal situations.
In Sweden, most people use “Hej”. It usually works in both formal and informal situations. In a formal situation “Hej” is used together with a handshake.
There are, however, many more ways of saying hello in Swedish:
Hallå!
Hallå där!
Hej hej!
Hejsan!
Hejsan svejsan!
Tjena!
Tja!
Tjenare!
Tjena mors!
Tjabba!
Morsning!
Morsning korsning!
Tjing!
Stick to the three first ones if you want to keep it safe.