Welcome! I'm relatively new here myself but in the past few months have soaked up a WEALTH of knowledge from this board. Please do not hesitate to post questions.
There are no bad questions. We all make mistakes, and it is especially easy to make them when starting out. Heck mistakes can be made by veterans too. So ask away. If unsure why your first shot wasn't so successful, let us know as much of the detail as possible... and we can try to help. There are a LOT of great people on here!
A few things I picked up since being a new: Of course there are a lot more tips, but a select few I can come up with now.
-Get a refractometer to test water salinity. Make sure it is calibrated! My first mistake i n the hobby was using a used refractometer that was FAR off calibration. I was mixing water FAR too salty for a healthy tank. Thank goodness I was only curing liverock in a trash bin at the time. If I tried to start a tank with that salinity, I'd be killing fish.
-Take things in stages, slowly. Marine aquariums need time to settle and adjust. Learn how to test your water parameters. Testing often is good early on. Once you have a more established system, you can get away with testing less frequently as you 'know' your tank.
Most of all. Have fun and enjoy the critters.