Measure the height of the wall where you want to hang the egg crate foam.
Cut a sheet of egg crate acoustic that matches those measurements, using the craft knife.
Apply a thin layer of acoustic foam adhesive to the wall or flat portion of the egg crate foam. Where you apply the adhesive depends on the adhesive you use, so follow the application instructions on the container.
Press the egg crate to the wall, making sure it's lying flat.
Repeat steps 2 through 4 until you have completely covered the walls and insulated the room.