Red Hat Linux is designed to use a three-button mouse. If you have a two-button mouse, you should have selected three-button emulation during the installation process. If you're using three-button emulation, pressing both mouse buttons at the same time equates to pressing the missing third (middle) button.
In this document, if you are instructed to click with the mouse on something, that means click the left mouse button. If you need to use the middle or right mouse button, that will be explicitly stated. (This will be reversed if you've configured your mouse to be used by a left handed person.)
The phrase "drag and drop" may be familiar to you. If you're instructed to drag and drop an item on your GUI desktop, click on something and hold the mouse button down. While continuing to hold down the mouse button, drag the item by moving the mouse to a new location. When you've reached the desired location, release the mouse button to drop the item.