Note: If you need help with how to download and install software programs, here is a tutorial:

A download guide for the a windows PC

A download guide for the mac


How to handle the error "Your security preferences allow installation of only apps from the Mac App Store and identified developers."

Unfortunately, SeaMonkey and Open Office are not in the mac app store. The Mac gatekeeper is giving you this error "Your security preferences allow installation of only apps from the Mac App Store and identified developers." If you control click the download, I think it will give you the option to override the gatekeeper. This process is described in more detail in :

https://support.apple.com/en-us/HT202491 Read the : "How to open an app from a unidentified developer and exempt it from Gatekeeper." section

Here is are the basic instructions: