If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Cut them off at the bridge!
Click to place the dynamite, then hit Ready to send in the enemy troops. While they're crossing, click the sticks of dynamite to set off explosions. Destroy as much of the bridge as possible while killing enemy units. Reach the target score (shown in the top right) to complete a level.