You can no longer use the sign-up code. As with Version 1.5(3411) on the Android system.
If you haven't been invited to play through Facebook, then you get to chose which server you want to play on. It's a good idea to chose one with a high number as this will be a younger server and existing players will be less established. See servers.
Once you're in the game, complete all the introductory missions. It'll take you a day or two, but you can't really do anything else, plus you'll get a lot of vital resources, Dark Matter and ships which will greatly accelerate your progress in the early stages.
Make sure you check your 'capsule' for bonuses. It won't be mentioned in the intro missions, but you usually get a bunch of bonuses when you start on a new server: shields, auto-navigators and resource containers. You can use these to accelerate your progress.
You will now have learned all the basics of the game, but galactonite probably doesn't make much sense and the intro missions probably skipped telling you that that Dark Matter can be used to instantly complete building upgrades and ship builds.
You now have a couple of planets, a few ships and thirst for war. Settle down though; attacking people in the early stages of the game is a great way to get yourself farmed. Your aim right now is to focus all your time and resources on getting Espionage Tech to at least level 7 or 8, and building Recyclers. The end goal of this is to start neb runs.
neb runs are the life-blood of your game. To support this aim, you also need to:
As soon as you have at least 4-5 Planets, each able to dispatch three Recycler fleets of 667 units, simultaneously, to the Mysterious Nebula, and you're hitting 120 explorations in a day, the only thing left to do is build your attack fleet. Build Destroyers. Lots of Destroyers.