If you were shooting a portrait in a darkened room and took one shot without it and then one with the snoot in place, you would see a marked difference between the two. The first shot would have a floodlit feel, while the snoot would create more of a spotlight and pick out a smaller area with the rest of the scene falling into shadow.
Crafting a homemade snoot is quite a simple task. If you happen to have an empty tube of potato chips around, you can use that. Alternatively, a cardboard tube designed to go through the mail is a good option, particularly if it has plastic end caps.
Cut the base of the tube out (the metal bases can be removed with a tin opener) and use some duct tape around the aperture to avoid sharp edges. Some more duct tape can secure that end of the tube to your flash head if required giving you an instant snoot to focus the light into a tighter beam.
That is great, but you can also make what is called a grid to focus the light even more. A grid is essentially a honeycomb disc that attaches to the far end of the snoot. Making one for your improvised snoot is quite easy. For a very small sum, you can purchase a box of large black plastic drinking straws.
Pack the straws into the end of the tube, get them all flat and then use a wide piece of adhesive tape to bind them all together tightly. You can use scissors or a bread knife to cut the bundle of straws down to a more manageable height (say, 50mm-75mm high). You can then insert the bundle into the end of the snoot for a highly controlled beam of light. You can now shoot intimate portraits or even use the snoot on your flash as a hair light.