How early should I go to the airport if it's my first time?

For a domestic flight, 2 hours prior to departure. For international flights, 3 hours. If you are unfamiliar with the airport or feel that you may require extra time, then add another 30 minutes and you should be fine.

Arrive at least 2 hours before a domestic flight, and 3 hours before an international one.

Depends on the airport.
I love airports. I go 3 to 4 hours early to have a few drinks, walk around, have a few more drinks and even have a nice sit down meal. Travel in the old days was glorious, glamorous and exciting. I don't like to be all hustle and bustle.

At Melbourne Airport, I would suggest three hours early. You have to check in - and there are sometimes queues for that depending on time of day and other situations - drop your bags off, and then you have to go through security, which for the international section is quite stringent, you have to get your passport checked and your exit card done, and depending on how many people this could take ages - like, upwards of an hour, especially if you're not well-prepared.

Plus, the duty-free and shopping area is really huge, there are plenty of great places to eat, it's really cool to walk around and investigate, so if you end up a little early, who cares?

For International flights, it's advised to arrive three (3) hours prior to flight.

Early

As you are travelling International you need to get to the airport at least three hours before the flight departs. You need time to check your baggage, get a boarding pass, get through Immigration and security, both of which can be time-consuming, and many planes start boarding 1 1/2 hours before departure.

At least 2 hours before flight departure.

I would suggest 4 Hours prior to departure as you need to go through a lot of processes and if you're new you will be slow and you might end up missing your flight.

Check your ticket. It should recommend how early to show up to the airport based on circumstances. Then normally add half an hour to that. But for your first time add an hour.