You can insert a gallery into any page or post by uploading the images you’d like to include on that page and then clicking the “insert gallery” link inside the upload pop-up once the uploading is finished.
There is also a post template for creating a gallery slideshow. To use it, just upload the images you’d like to include in the slideshow. Don’t insert a gallery or the individual images into the post. Then in the right hand column, choose “Gallery Post” from the post template drop-down. That will create a slideshow at the top of your page like this one: