Office Store FAQ - Microsoft Support
Add-ins are mini applications that extend what you can do with Office, Microsoft 365, and SharePoint 2016. For example, with Office add-ins you can use Wikipedia without leaving Word or get directions and maps right in Outlook. Add-ins are available for Access web apps, Word, Excel, Outlook, Project, PowerPoint, and SharePoint.
Using Access or Excel to manage your data - Microsoft Support
To find out which program is best suited for the tasks that you want to accomplish, it may help to compare the benefits that each program has to offer regarding data storage, data analysis, multi-user collaboration, and security.
Video: Manage Store add-ins - Microsoft Support
Use a Store add-in to add new tools or features to Office. Select Insert > Store. In Outlook, select Home > Store. Browse the list of Office Add-ins or search for one in the search box. Select an add-in to learn more about it. Select Add or Buy for the add-in you want. In Outlook, switch the setting to On or select Get it.