When to choose SharePoint Online
Choose SharePoint Online, when your organization subscribes to that service in Office 365 (Enterprise, Education, Government and DvNext). You'll enter your work or organization account to continue the sign-on process. Office 365 Personal and Home subscriptions do not include SharePoint Online.
When to choose SharePoint Server
Choose SharePoint Server when your organization provides SharePoint 2013 or SharePoint 2016, which have a different login process than SharePoint Online. You'll enter the web address of your SharePoint Server to continue the sign-on process. The web address, also known as a URL, may look like http://portal. This option is sometimes referred to as SharePoint On-Premises or On-Prem.
Note: It's likely that access to your SharePoint Server will be restricted by your organization. For example, you may not be able to reach it when you are not on the corporate network.
If you're still unsure which option to choose
If you're still unsure, ask someone at your organization if you have SharePoint Online in Office 365 (Enterprise, Education, Government and DvNext). If not, ask for the web address of your SharePoint 2013 or SharePoint 2016 server. If none of those options work, you may be able to identify the correct option from a web browser when logged in to SharePoint. Read below to learn how to identify SharePoint Online, SharePoint 2016 and SharePoint 2013 in the browser on your PC.
Identify SharePoint Online from your PC
You'll know you're using SharePoint Online when you see the words Office 365 to the right of the App Launcher in full screen on your PC.
Identify SharePoint 2016 from your PC
If you see the word SharePoint to the right of the App Launcher without the words Office 365, you're using SharePoint 2016.
Identify SharePoint 2013 from your PC
If you see the word SharePoint in the upper left of the screen without the App Launcher or the words Office 365, you're using SharePoint 2013.
Tip: The SharePoint mobile app for iOS will be available from the Apple App Store in June 2016. Android and Windows versions will follow.