OK, thanks.
From the specs, that sounds like an iMac (21.5-inch, Mid 2011), which only supports up to macOS 10.13.6 High Sierra.
You can check on applications that launch at login here: > System Preferences... > Users & Groups > your user > Login Items. Also, ani antivirus applications would be in the Applications folder, and most would have a menu bar icon if they are running all the time.
You have plenty of free space, so that isn't the issue.
-Photos: Can be somewhat slow when opening if you have thousands of Photos, and if you use iCloud Photo Library/My Photo Stream/iCloud Photo Sharing.
-Word: Depending on the actual version, older versions of Microsoft Word can be painfully slow since they came out way before and aren't fully compatible with High Sierra.
There isn't any easy way to drastically speed up your iMac. Another 2 x 2 GB of RAM would help a little when you are running several applications simultaneously, but not a very noticeable difference.
Here is a good basic troubleshooting guide:
The X Lab: The Spinning Beach Ball of Death
Other causes could be a failing hard drive, older/incompatible software versions, antivirus with on-access or real-time scanning enabled, etc.
See if any of the steps in the article help.
C