You can create a slice object by drawing it with the Slice tool or by inserting a slice based on a selected object. The lines extending from the slice object are slice guides, which determine the boundaries of the separate image files into which the document is split on export. These guides are red by default.

To insert a rectangular slice based on a selected object:

1. Choose Edit > Insert > Slice. The slice is a rectangle whose area includes the outermost edges of the selected object.
2. If more than one object is selected, choose how to apply slice guides:

·        Single creates a single slice object that covers all selected objects.

·        Multiple creates a slice object for each selected object.

To draw a rectangular slice object:

1. Choose the Slice tool. 
2. Drag to draw the slice object. The slice object and slice guides appear on the Web Layer.

Note: You can adjust the position of a slice as you drag to draw it. While holding down the mouse button, simply press and hold down the Spacebar on the keyboard, then drag the slice to another location on the canvas. Release the Spacebar to continue drawing the slice.