before I had my DSLR I had a Sony H5, which is similar to an S3 IS. I learned alot from this website which I think will help you with the S5 as well (buttons and controls are in different place that's all really..)
http://www.aakatz.com/whitepaper/
Av mode is a great place to start, full manual isn't much harder, but I would keep autofocus on auto (manual focus on the H5 was useless). But don't be afraid to experient in manual mode. If you get in a jam you can probably just switch it back to Av or auto and be ready to shoot again.
