Most of you would know that you can insert slides from another presentation by using the Slides from files menu option in the Insert menu. This is another (harder) way to do the same.
Open the presentations you want to copy/move slides to and from. Click Slide Sorter on the View menu. On the Window menu, click Arrange All to display both presentations.
Click the slide you want to move, and drag it to the other presentation. When you drag and drop slides between presentations or from PowerPoint to other apps, Windows moves the slides instead of copying them. To keep the slides in the original presentation as well, press Ctrl while dragging and dropping.
To select multiple consecutive slides, click on the first one, then click on the last one while pressing the Shift key on the keyboard, and all slides between the first and the last will appear highlighted.
Note: To select more than one noncontiguous slide, press Ctrl while you click.