Voting in the federal election is compulsory. If you can't make it to a polling booth on Saturday 21 May, you can vote at your nearest early voting centre up until 6:00 pm on Friday 20 May.
Find your nearest polling booth using the Australian Electoral Commission's interactive map - https://www.aec.gov.au/election/voting.htm#start
More election information can be found at www.aec.gov.au or cal 13 23 26.