The Atom 2.0 is a very easy computer to learn how to use. I have one and have been using it for about four years. If you are diving air then it's almost as simple as hit the water and it will give you depth and time. If you are diving Nitrox then you enter in your percentage for the mix you have, hop in, and it gives you depth and time correct for the mix you are using.
You don't mention if you also got the transmitter. If you did, then attach it to your first stage an now you get depth, time and your remaining air pressure. If you do have the transmitter, in my opinion, don't bother with the buddy pressure check. It's more trouble than it's worth.
I have over-simplified how an Atom works, obviously. There are many settings that can be changed by the user: alarms, preferences etc. The manual is a great place to start. Once you have reviewed it plan a dive or two based on tables (you did say this is your first computer). Dive according to your tables and when back on land read your computer and see how it stacks up to your table calculations. The Atom also logs your dives and your surface intervals so filling out your log book gets easier, especially if you are on a crowded dive boat in three to four foot seas!!
Enjoy the computer. It can grow with you as your diving skills advance. Three gas mixes, multiple transmitters=more possibilities!!
Happy diving!!