There are two ways to add a 
Component to a 
Form or 
Page:
1. Linked
A Component added as a Linked Component can not be modified in the Page or Form. The Components themselves can be updated and then redeployed back into any Form or Page into which they have previously been inserted.
Changes to the Component do not update Forms and Pages automatically and must be redeployed by clicking 
Deploy in the Component's Editor.
Although the structure of a deployed Component cannot be modified in a Form or Page, its properties can be overridden. For example, a Control could be made Display Only in the Page. Local overrides made in one Form or Page do not affect the Component itself or other Forms or Pages it has been added to. Local overrides are not removed by a redeployment.
Once inserted, a linked Component can be converted into an Embedded Component.
Linked Components are useful for aspects of UI that are consistent across an application. For example, headers, footers and menus.
2. Embedded
An Embedded Component is designed in the Component editor but maintained locally. Once a Component has been embedded into a Form or Page its link to the original Component design is lost and changes are made within the Form or Page.
Once embedded, a Component cannot be converted to a Linked Component.
Embedded Components are useful in cases where you have similar UI that you expect to customise once they are in place, for example, popups.