Minecraft is a survival game. Basically all you do is survive, unless you play in creative mode (which allows you to build freely with any blocks of your choosing, through the inventory screen!) Minecraft is also a building game.
You can register with any of your emails, it does not matter because you get to choose your username- it will not be your email username when you register, unless you choose it to be so. Be sure to pick a username you like; you can't change it once you pick it, as of right now.
You will have to do LOTS of crafting and farming. I would check the minecraft wiki's crafting section so you can learn how to craft every day items, such as swords or wood axes or pick axes, even hoes. You will need those four items in order to play the game properly, so you should definitely learn to craft them! You can use pick axes to mine into caves which include ores such as iron, coal, and other treasure ore such as diamond or gold. Coal is an absolute necessity if you need to craft torches- torches are every day items as well. You need to know how to craft them too.
Wood is also a necessity. You need wood for everything- creating tools, building a house, and creating furniture for your house. When you first begin the game you will spawn without tools, but you can punch trees to obtain wood, and then you can create tools!
At night time, monsters (commonly referred to as 'mobs') come out. It is recommended you find shelter on your first day, and set up a small camp so you can survive the night. Once the sun rises, most of the monsters will burn from the light, such as Zombies and Skeletons. Creepers and Spiders do not burn from the light, but they will despawn if you leave their area. Spiders are friendly in the day and will not harm you, but creepers and other mobs will attack you on sight.
However, mobs are immune to catching fire if they are in a body of water. Mobs also will not burn from sunlight if they are in a shaded area. You can lure them out and they will catch fire. Mobs drop items that can help you advance in the game. They naturally spawn in darkness- such as caves. This is why you need torches; if you build a house, and do not light it up, they may spawn inside. If you light up any area in the game with torches, they will not spawn there. If you die, all of your loot in your inventory will fall out where your death occurred. It's easy to get lost in the world; be careful and try to keep track of where you are.
I would recommend playing survival mode first, in singleplayer mode, so you can learn the game. Multiplayer servers usually have lots of people in a big world that get together to do PVP's, other games, or even roleplay, and they all generally know what they're doing- so you should learn as much as you can, especially the basics, before you play on a server!
As for getting into a Multiplayer server, you can do so by finding IP's through the internet. IP's are a set of numbers that is basically a key into someone else's Minecraft world. It is the creator of the server's computer address. The IP connects you to their world. Once you find an IP- you can find them anywhere on the internet really- you have to click 'Multiplayer' on the starting screen, and click 'Add Server.' Two entry fields will come up- the 'server name' and the 'server address.' The Server Address box is where you enter an IP. You can leave the 'server name' box as it already is, but you have to enter the IP into the 'server address' box so you can play on other people's servers!
I hope this helped you! I highly recommend you read up the Minecraft Wiki so you can learn the basics about the game :) There is also information there about Multiplayer Servers.