[shubham]

can you elaborate your problem so that i can help you.

[shubham]

Process Builder and WorkFlow Both are Use to automate the process. Like firing email or update records when we meet certain criteria.
The process builder is more advance and gives us more option then workflow.

[shubham]

In General if you want to understand Feed, feed is like a post (like a fb post) which you can share, like, comment and the object which store this is feed item.

[shubham]

Hi Marziya to add a button in email template either
Use a Visualforce email template or Custom email template.
And add button using button tag.