These are the options that you'll see when sharing files or folders in Office 365, OneDrive, or the OneDrive sync folder in Windows Explorer or macOS Finder. If an option is grayed out, check with your administrator - they may need to configure external sharing.
In Link Settings, you can choose who your sharing link gives access to:
Anyone creates a link that anyone can use to access the document or folder, even if they're not logged in to Office 365 or OneDrive. Use this to share with anyone, inside or outside your company. This link can also be forwarded around to anyone.
People in <organization> creates a link that only people in your Office 365 organization who are logged into Office 365 can use to access the document or folder. Use this to share with anyone in your Office 365 organization. This link can also be forwarded to others, but only works for people in your Office 365 organization. Note that this link will not work for Guests in your Office 365 organization nor will it work for people who are not signed in.
People with existing access returns a link that can be used by people who already have access to the document or folder. It does not change the permissions on the item. Use this if you just want to send a link to somebody who already has access.
Specific people creates a link that only the people that you specify can use to access the folder or document. If you click this option, enter the names or email addresses of the people to whom you want to give access to the folder or document. Use this to share with specific people only, who can be inside or outside your Office 365 organization. The people you share with cannot forward this link to others.
Once you have selected who you want to give access to, select or clear the Allow editing check box depending on what type of access you want to allow, and then click Apply.
When you click Share, you can send a link to a person or group that they can use to access the folder or document. Just enter their name or email address, optionally type a message, and click Send.
To change the link type (who can access the folder or document) click the drop down menu to go to Link Settings.
Clicking Copy link creates a link that you can use to share a document or folder and copies it to your clipboard. You can change who the link gives access to by clicking the drop down list at the bottom of the dialog and going to Link Settings.
If you want to change who has access to the folder or document, on the Send Link page, click the ellipses, and then click Manage access to go to the Permissions page. On the Permissions page, you can update or delete the access links that you have created.
Note that if you want the document to appear in search results for the person you're sharing with, you must give them direct access to the file rather than sharing with a link.