At the start of the level, the first thing you will see is a Goomba Tower, with a Fire Flower on top of it, so go ahead and grab that. Ahead of that is a clear pipe, with a Fire Bro on the other side. While you could try to time a fireball through the pipe, you can simply jump on top of it to go to the other side, either ignoring the enemy or tackling it there. At the next set of clear pipes, you have the same opportunity, but whatever you do, make sure to go through the middle portion to collect Green Star #1. Along the little piece of wall on the other side of the clear pipes, you can find a hidden ?-Block that contains a 1-Up Mushroom.
The next obstacle for you will be Fire Bars that are spinning around some ?-Blocks. Stand on top of the second one here and perform a Ground Pound, only to be shot into the air, where you can retrieve the Stamp. From this height, you should have a clear shot at jumping on the Fire Bro at the top of the Goomba Stack, so do that to make a Warp Box appear. If you didn’t jump from the tall tower, then you will need to reduce the Goomba Stack until you can reach the Fire Bro. Either way, the Warp Box will take you to the Checkpoint Flag.
Right by the flag are some invisible ?-Blocks, acting like stairs to the top of the wall. Climb to the top of the wall, then head left to find a green pipe, leading you to another ball and flip panel puzzle. Here, you want the right most to be on red, then you’ll need both sides in the middle, and red in the bottom left. This will guide the ball to the switch in the corner, letting you grab Green Star #2. Back in the main area, either cross via the walls or sneak past the Thwomps, grabbing the power-up from the one ?-Block. There will be two clear pipes here, which across cross underneath the lava, with a Fire Bro on the other side.
Try to time some fireballs, then try to avoid touching the Green Star Ring. The reason for doing this is to clear the area first, which can easily be done by hitting the POW Blocks. Once you do this, hit the ring and collect the coins to get Green Star #3. Take the pipe to the last segment, where a Fire Bro will hop back and forth between Goomba Towers. You only need to defeat the Fire Bro to continue, so do whatever you need to bring it down. Take the Warp Box that appears after, landing you in the Goal Pole area.