Leave the Speeder where it is and look around on foot. There’s plenty of studs around here. Go up the screen until you reach the gate. Use the Force on the Grey bricks to the right to form stairs that’ll let you reach 3PO’s panel that will open the gate. If you want to, go back for your Speeder now and cross it.
When you reach the square, you’ll have to use the parts around to build an AT-ST walker. First switch to R2 and open the door to the left of the blocked passage. Destroy the two barrel to the right and switch to 3PO to open the door near them (first you have to make a footbridge for him). Use the Force on all of the walker’s fragment to complete it. You can’t go wrong with it, so don’t worry.
When you’re done with the walker, a stormie will enter it (now that’s just rude). Switch to Ben and Force-pull him outta there. Enter the AT-ST yourself and use it to destroy the blockade. Go further, defeating the stormies. Jump out of the vehicle and go through the door.
You’re in the Cantina now. Switch to Luke and shoot all 4 force field generators. Stand on 4 buttons near the entrance. You’ll see a cut-scene now. When it comes to an end, you’ll be controlling Han and Chewie. Go to the right and use the passage marked with the greek arrow. Grapple up to reach the upper level. Use the bricks to build another grapple point and use it.
Go to the left, grapple across the street. Use the lever to get a crate, push it down and to the end of the track. Shoot it a few times and you’ll be able to go further. Defeat the stormies and mount one of the Dewbacks. Place it near the arcades and jump off it – it boosts your jumping height so you can reach the upper level. Go forth to the next section.
Now you’re at the Millenium Falcon’s hangar. You’ll face a boss fight here – this time it’s the imperial spy. He’ll summon waves of stormtroopers to his side. At first you won’t be able to get to him, so just get rid of the stormies. By the third wave he’ll make himself available, slash him a few times and you’re done. Board the Falcon.