The Sliced View panel displays an alternative view of items selected in the main display. It is especially useful with mammalian genes which can span vast regions of genomic sequence but which are comprised mostly of intronic sequence. The The sliced view aims to give you a higher level summary of gene structures by condensing the intronic regions and allowing you to focus on the exons, relative to each other.
The following image shows how this works. The top panel is the IGB main display window shows the normal, non-spliced view of a region containing what appears to be two overlapping genes from a cow: GBN4, which contains an enormous five prime intron that completely encompasses another gene, ZNF639, which encodes a zinc finger protein. The Sliced View panel on the bottom shows these same two genes, but with much of the intronic sequences sliced outreduced to 100bp. The places where the slices were made appear as black hash marks below the axis in the Sliced View. Note how the sliced view makes it easy to see both gene structures simultaneously, whereas in the main view ZNF639 is so small it is impossible to even see the number of exons it contains. Wiki Markup 
You can enter the size you want the introns to be set at by changing the number in the Slice Buffer (default is 100). By unchecking the Slice by Selection box, you can move the main view to another region of interest, and click on other features without changing the sliced view.
Another feature that the Sliced View panel supports is finding open reading frames (ORFs) and stop codons. For details on using this function, please see Showing ORFs and stop codons.