We've all been there. Our first time playing as a shaman and we have absolutely no clue of what we're doing or what our menu means. The other players aren't helpful either, as they just yell at you, calling you a "noob", angrily yelling at you to "PRESS B!!!", or even trying to get you banned. NO LONGER! We shall learn how to play the Shaman!
Remember, the Shaman is the player with the most points at the end of a round, if that map requires a Shaman. Some maps will require two Shaman, which is most commonly 1st and 2nd place (though I have noticed that 3rd place is picked often as the 2nd shaman).
First off, you will need to know the functionality of each item in your "inventory" (You have an infinite amount of each item, but spamming them can crowd the map).
1. Arrow - The arrow has no physical effect on the world. It is used as a tool to instruct mice exactly where you need them, such as to Spirit them over a gap. You can use this anywhere without needing to be close.
2. Spirit - This magical effect is a force field that will send anything, being mice or items, flying away from its center. The distance from the center will determine its strength. This is best used to jump mice over gaps, knock off ENEMY Shamans, or remove troublesome mice from the map. You can use this anywhere without needing to be close.
3. Balloon - Your childhood balls of plastic now serve a purpose! The balloon can be spawned to help support weak bridges, lift Airships, and even lift mice in some occasions. The balloon is very risky and is not commonly used. You must be close to the Balloon to spawn it.
4. Rune - The rune is a flying stone that will push objects and mice. It is incredibly risky to use and should only be used for certain occasions by skilled Shamans, such as guiding off-target Airships back on course. You must be close to the Rune to spawn it.
5. Box - The Boxes, small and large, are widely used as a Shaman, next to the more commonly used Planks. Boxes have several functions, such as building Airships, making temporary stairs, or blocking ENEMY Shamans' holes, with the assistance of an anchored Plank. You must be close to the Box to spawn it.
6. Plank - The Planks, small and large, are the most commonly used object in Transformice. They are used to build bridges, Airships, ramps, anything that can cross the mind. Planks are almost ALWAYS utilized with the B and C commands, which we will cover later. You must be close to the CENTER of a plank to spawn it. (For large planks, this is usually just by the end of the plank.)
7. Anvil - The Anvil is a heavy item used to weigh down unanchored objects or Planks. Certain maps may prove much more successful if an Anvil is used to weigh down one end of a large platform so mice can safely cross. You must be close to the Anvil to spawn it.
8. Ball - The Ball is an item used to bounce mice high in certain maps where the only other alternative would be Walljumping. When the ball is placed on certain maps, mice will have about 2 seconds to get in position before the Ball explodes, acting like a very powerful spirit. By pressing Spacebar on the Ball, the ball will become transparent, so mice will be able to go through it without needing to worry about jumping on top of it. This is used to reach cheese that is high in the air. You must be close to the Ball to spawn it.
9. Trampoline - The Trampoline is a small Plank with a bouncy top. Mice that jump on this repeatedly will go higher and higher, making this very useful to jump over walls or reach high platforms. By pressing C, you can attach the Trampoline to another Plank in the center to keep it from moving. You must be close to the Trampoline to use it.
10. Drag - The Drag is a powerful, flying ball that will force anything it runs into towards that direction. The Drag has 3 types, Left, Down, and Right, though it can be rotated to point any direction, including Up. It is used to free trapped mice, kill ENEMY Shamans, and to kill troublesome mice. You must be close to the Drag to spawn it.
11. Portal - The Portal is a field that can take mice from one point to another. It doesn't matter which hole is used for entering, it works both ways. This is used to get mice over impassable walls, reduce risk from falling, or to save time. Portals are only available on a few maps. You must be close to Portals to spawn them.
Those are your items, and you already now know more than the average beginning Shaman. But can you use them correctly?
By popular request: Functions of the Hotkeys

Now, we've all been yelled at to "PRESS B" or "PRESS C" or "SPACEBAR NOOB LOLOLOLOLOLOLOLOLOLOLOLOLOL" You look at the help menu, but it's like reading Japanese. Unless you know how to read it. Then it's French.
Watch the following video with this in mind: The B button creates the plank with the RED DOT. This dot stays in that spot, making a loose platform. By pushing Spacebar afterwards, mice can go through it. Then you may use the CONTROL KEY to rotate it. By placing this close to a wall, under center, you can create a "solid" plank.
Now take a small plank and press C (You can press C multiple times to get the YELLOW DOT on the side). By attaching this to another object (Usually a plank), it will connect to that object. By using the simple commands, "B, C, and Spacebar", you should have no problem creating bridges, which are the solution to 95% of maps.
http://www.youtube.com/watch?v=jsrtuhiWzEY
There are 2 other commands, V and N, but these are pointless for now, and I have never had a use for them yet.