Link Types Fields
Link types fields allow the users to enter links to the items, external URLs, anchors, email addresses, or JavaScript functions.
Droplink
The Droplink field type allows the user to select a single item from the list specified in the Source property. The list consists of children of item that is specified in the Source property of the field. It is very much similar to Droplist. For an end-user, it works like Droplist but for a backend developer, Droplist will store the name of the item while the Droplink will store the ID of the item. Moreover, droplink does not support the rendering of the field. The source of Droplink can be XPath query, GUID, and Item Path.
Droptree
The Droptree field type allows the user to select a descendant of the item that is specified in the Source property of the field. Droptree shows the items as a tree view instead of a dropdown. The user can only select a single item at a time. It shows a complete Sitecore Content Tree if the source is not provided in the Source property of the field. The source can be XPath query, GUID, and Item Path.
General Link
The General Link field type allows the users to link an item, an URL, an anchor, an email address, or a JavaScript function. It allows users to insert an internal link to Sitecore Content Tree or an external URL or a custom anchor tag or an email address or a user can insert a JavaScript function. General Link types support the field render.
General Link with Search
This field is similar to the General Link type field but it has an extra feature for searching named "Search for a link". This field is used to search for an item that is stored in the Sitecore Content Tree. General Link with Search support the field render.
Version Identity
Version Identity field type is for Sitecore internal use only.
Version Link
Version Link field type is for Sitecore internal use only.
References
Field types in Sitecore - https://learnsitecore.jprajapati.in/2017/03/29/field-types-in-sitecore/