Welcome to the first level of Super Mario 3D Land. This isn't too hard to beat.
Before the checkpoint flag
Start by running to the right. Jump on the ledge. Hit the ? block if you want to, but all it holds is a coin. Now, either go over the white bridge or grab the coins/kill the Cheep Cheep and then go over it. It doesn't matter if you fall in the water, just jump back up. You can kill the Goomba that awaits you by jumping on its head. The ? block between the two bricks contains a Super Leaf (unless you got hurt by one of the two enemies you've encountered so far, in which case it will be a mushroom). Grab it to become Tanooki Mario (or Super Mario if you grabbed a mushroom). There is now no white bridge. Well, there is, but it's broken. Again, it's OK to fall in the water, but unless you want the Star Medal, run away from the camera, jump up the staircase-like blocks and jump to the other side. If you want, you can roll/duck-spin the blocks lying on the ground. The one closer to the box has a coin, the other one has nothing. If you want a 1-up mushroom, run towards the wall and to the right. There will be an opening. Run through it and towards the camera. You will see the words 1-up appear, which means that you've grabbed it. To get out, either go back through the opening or keep running towards the camera and spin/roll into the crate that stands in your way (this is also a way in if, when over the bridge or having grabbed the first Star Medal, running towards the camera and jumping over the fence). You can now choose to either wall-jump back up or to run left, jump over the fence and on the blocks that lead you back up). If you go back to the opening, climb up the tree and jump on the blocks, run towards the camera and get another extra life. When you're back, you can get the three coins in the long ? block and use the platforms to get up. There is another Goomba awaiting you. Choose what you do with it. While we're here, I'll tell you about the trees. Run to the left and run towards the two trees next to each other. When you climb to the top of the one to the right, a Super Leaf will appear. While you're here, it's recommended to hit the checkpoint flag. (When you run to the left, you can jump off the top of the first tree you find to get to the music blocks and at the top, there's a pipe. You will appear in a small, bizarre room containing a Star Medal. If you turn on the 3D, you'll now find it easier to work out where the Star Medal is.