Welcome to World 3! This world is based on forested and aquatic environments. For example, this level takes place at a beach.
The level begins on top of a hill of sand. Cheep-cheeps will frequently jump out of the water this level, so be careful not to be hit from above. On the next hill over, you'll find a Super Leaf. You'll then see the first barrel of the level. Barrels act as floating platforms, but sink as they're stood upon, so be quick! A Gold Ring will appear, which makes the Cheep-cheeps leave trails of coins. Go through it and continue onwards. Be aware that they can still hurt you though. As you come across a group of three barrels floating in a row, you'll see the first star coin floating overhead. Jump on one of the cheep-cheeps while it's in the air to get the extra height necessary to grab it.
On the next platform, you'll see several blocks. The one on the far right contains a switch. Hitting it causes coins to fall out of the nearby pipe, a nice present. After you reach the checkpoint, you'll see a pipe with a piranha plant above. Get on the Ferris Wheel of platforms, and then wall jump off of the pipe or the adjacent wall. You should get your second star coin. The nearby ? block contains a Fire Flower.
Continue moving right, and you should see a Gold Ring. Go through it to get more coins. On the next hill will be two blocks. The right one contains a Super Leaf. Jump over the enemies and go down the first green pipe you see. Inside is a switch that releases a bunch of coins to collect. Moving back to the surface, go onto the barrel to the left and let it sink a short distance to grab the final star coin.
The rest of the level is fairly simple. Go into the Gold Ring and run over the hills, dodging the fish that jump out along the way. You should soon reach a green pipe. This takes you to a small new area, where you can jump onto a platform to reach the top of the flagpole.