1) Smoke Test is to perform whether the critical functionality of the application is working fine or not.
It is done Software developer or tester.
It is called as subset of Acceptance testing.
It is done on every build release.
It is test the over all functionality of the application.
It is used to check the Stability of the application.

Sanity Test is used to perform Particular functionality of the application is working fine or not.
It is done by tester.
It is called as subset of Regression testing.
It is done on every bug or defect fix.
It test the particular functionality which the bug is raised or defect is found.
It is used to check the Rationality of the application

2) Agile It is a SDLC Model.
It is a iterative and Incremental Methodology.
We can use Agile when the requirement is not stable and it can implemented in large projects.
So that we can able split in small unit/module that is know as sprint.
It is like a framework It have some protocol to follow Agile.
For implementing Agile we have some tools like Scrum, kanban, Extreme programming(XP).
In scrum We have Epics and user stories.
IN Scrum we have Scrum team, Product owner, Scrum Master.
Scrum master will conduct Scrum meeting, In that Scrum meeting we have
Sprint Grooming.
Sprint planning.
Daily Scrum.
Sprint review.
Sprint Retrospective.
Sprint backlog-> that the List work assigned in the Sprint should be done with in that sprint.

3)
In project each every requirement that need to be tested is a User stories for example--> login page, User name, Password, log in button,etc.. this caled user story.

where as Epics Are the collection of all user stories.
for Example --> Login, Search item, Buying Item, Payment, conformation of order, tracking order, etc... This is called as Epics