Blocks will appear in the left hand column, up to three at a time. On the right is the barricade, which is continually eaten away from the bottom. Place blocks from the left on the barricade. Blocks can be rotated with the arrow buttons or the mouse wheel. The aim is to keep the barricade from being destroyed by making complete rows of material. These are harder for the enemy to destroy. The more rows you fill at once, the stronger the barrier.
The following gadget modifications are related to Barricade or directly provide bonuses during Barricade.
The following is text from tutorials that appear in the game.
The Basics of Barricading
"To barricade grab and place pieces to create solid rows to block their advance. Enemies will continuously break down your barrier, so keep them blocked!"
"Placing pieces that create two, three, or even four rows at a time will create stronger barricades. These will take more enemy bashes to fully break down."
Keep it Coming
"Your friends are counting on you to keep the enemies out. If your barrier is broken down, the enemies will soon come bursting in!"
- Planning in advance is helpful. Set up the board in such a manner that you can create multiple rows with a single piece. Creating two rows at once is significantly better than creating single rows twice. For example, try to leave a single, straight vertical gap in your rows so that a straight piece can fit into it and complete up to four rows at once.