ACTIONS IN SALESFORCE

==> Actions are similar to buttons and links which give users access to do things in a go.
==> using these actions we can create or update a record, log a call, send an email or do custom things like opening visualforce page or lightning component.
==> All the actions have their own action layouts which specifies the fields that will available on that particular action.
==> These actions can be used on salesforce classic, salesforce 1 and salesforce lightning.

Difference between object specific actions and global actions

Object specific actions                         |                  Global actions
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1. These actions are created in the           1. These actions can be used globally on the chatter feed
context of the particular object                     page, home page and groups page

2. Automatically gets associated with     2. Never gets associated with  a record
a record

3. Use when you only want this action    3. Use when you want to be displayed everywhere and
to be displayed on records detail page        wherever actions are supported

4. Can only be added to page layout        4. Can also be added to global publisher layout which
of the object on which it is created               controls actions on chatter feed page and home page

Points to remember:

--> Action type cannot be edited once an action is created.
--> Global publisher layout can only have global actions.
--> The new records created from the global actions are not related with any other records.
--> Action layout always have universally required fields.