I think templates are awesome because they are a jumping off point on a layout... If you are using PS, you can use clipping masks to cut your photos into new shapes, and to cut your papers into shapes that the template gives you.
Templates are really great for helping you learn about scale and how large a photo can be or should be. Sometimes they help you achieve cool shapes across a page that you wouldn't have necessarily thought of yourself.
They also give you a jumping off point!! When I started using templates, I would use all the shapes and strips the template gave me and not much else... but my layouts had better composition than they would had I just thrown a couple photos on a page. Now that I am a much better scrapper and more accomplished user of templates, I take things out and add things in and make things smaller or bigger to match how I feel... These days, I almost always start with a template but by the time I'm done with the page, you can't hardly see any of the template left...
As far as the how do you go about using them... that really depends on which program you are using to scrap in...
If you are using Photoshop or PSE, you should be able to place your photo or paper in the layer just above the layer you want it to clip to and hit alt-control-g on your keyboard... This will clip your paper or photo to the shape of the layer of the template. Do this over and over until all the layers have papers or photos clipped to them. Add drop shadows and/or extra elements and you're done!!
In Paint Shop Pro, this is more difficult but can be done. You have lots of options actually in PSP of how to get the job done. My favorite is this: You can use the magic wand, make the layer of the template you want to clip your paper or photo to the layer you are on, and click your magic wand in a space where there is no shape. This should bring the "marching ants" around the shape of your template layer. In the layer palette, click the layer of the photo or paper you want to clip to make it the active layer and click on your keyboard Control-X for Cut (or go to Edit, Cut). This will cut away your extra photo or paper... Again, do this for all the shapes, and add drop shadows for a completed layout.
PSP is a little less forgiving than PS for using templates. It won't allow you to uncut a photo or a paper once you have moved on to the next layer. PS and PSE do allow you to undo a clipping mask much later so I prefer using templates in those programs. Either way, templates are an awesome scaffolding to get a feel for scrapbooking and to learn some neat features in your program of choice!!