Hi Sunkari, I'm no expert but hopefully this gets you on the right track.
Sunkari wrote:What is difference between Power BI embedded(link) and Integrate a Power BI tile or report into an app(link)?
Embedded can only be used for outside your own organisation (i.e. you are a software provider), and it does not use Power BI accounts. I attended a recent Roadshow - it is very promising but in early stages.
You manage the access via a secure key inside your application. The billing is on a per render basis. Currently, your datasource needs to be Azure SQL, Azure SQL Data Warehouse or HDInsight and it works only in DirectQuery mode. This should expand to cached mode and / or other cloud data sources over time.
Power BI Tile or report in your app, as far as I see in your link above, it is Azure AD authentication. You would take this approach if you have internal users and if they are signed into your app or their computer with their AD credentials. The billing is by subscription.
Power BI embedded(link):
Can we use this feature for integrating existing dashboards into external application?
There are a number of steps to get started. Embedded only supports reports at the moment, not dashboards yet. Support for dashboards will be coming later apparently.
You upload reports by uploading a .PBIX file using the API.
If yes, then how security will be handled?
Check out this blog post for embedded plus this for information on the security / authentication model. The security is currently applied at the Workspace level I think.
Every user, who has access to external application requires Power BI Account?
No. It does not use any PowerBI account for the user. You have a key that you generate in Azure for your application and then you (the software vendor) are charged per render.