When you click on an effect in the Pixel Editor's sequencing grid, the upper-left window will display thumbnails of effects used in the sequence on similar props. You can click on any of the thumbnails to make it the current effect (plays back on the right-hand window and changes the text below the Effect button):
This means the effect is ready to be placed in the grid. Select some blank cells in the grid and right-click to turn the cells on, ramp up, or ramp down (or use the equivalent shortcut keys). The effect that is playing on the right side will be used to populate the selected cells.