how to insert the See All link in a drupal view block i created a  News block that display only 3 lasted news, and i want create a button "See All News" 
how i can do it ?
In the footer section of the view add a global text area with the link of the See all news.

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Once you are done adding a field in the footer, save the view and the See all news link would work as expected.

For creating the Read more link


Go to the body field of the news.
In the Rewrite Result, you have a checkbox "Trim this field to a maximum length". 
Once you check the checkbox, you have the option to "Add a read-more link if output is trimmed.". 
Add the Read more text and use the [path] token for getting the path of the node.
Save the view and the Read more link would be there for all the news that you have.


Adding an image to help you in a better way: