What is External ID and Why it is used in Salesforce?

What is External ID and Why it is used in Salesforce?

I have divided this video into following points:

- What is an External ID in Salesforce?

- What is the use of External ID in Salesforce?

- How to set a field as an external ID?

- Which datatype fields can be set as an external ID?

- How many fields can be marked as an external ID in a single object?

Hope you enjoy the video and feel free to comment down on the bottom if you have any question.