That is what is referred to as the "spinning beach ball of death"...
"Occasional appearances of the beach ball can be expected. Depending on your Mac's current workload, even common tasks may temporarily overtax your Mac's resources, such as its CPU or available RAM. For example, opening complex applications, video encoding, or syncing large files with iTunes® may result in a brief appearance of the SBBOD, especially if other applications are also busy. Nevertheless, the SBBOD can indicate that an application or a system process is frozen, hung, or grossly inefficient."
From here > The Spinning Beach Ball of Death
Try using fewer applications at the same time.
How much free space on the startup disk? Right or control click the MacintoshHD icon. Click Get Info. In the Get Info window you will see Capacity and Available. Make sure there's a minimum of 15% free disk space.