Lessons learnt document is nothing but base document
Those may be URS/FRD
or use cases which makes u To learn about the application

In brief Lessons Learnt are usually the DO's, which proved 
us wrong and eventually turn out to be DON'Ts for the next 
assignments.

Lessons learnt document is a document generated as a 
feedback for the client and the vendor. This clearly 
explains the functional issues that came along in the 
project and how they could have been avoided.
It gives details on some of the new practices followed 
which were successful and cost saving so that they can be 
used in future.
In short this document should provide a guideline so that 
the same problems do not get repeated for the next project.

This is not answer, pls send me example document for this.

Is a document at the end of project phase. this explains the
various pains the team had to undergo and how and what they
did to resolve the issues. This document also serves as
knowledge sharing between projects.

This is the document drafted by the team members at the end 
ot the project phase. This document mainly speaks about the 
challenges faced and the lessons learnt from the project. 
Ex:the docuemnt contains like i learnt from the project How 
to be good team player and How to be an assertive perosn , 
some thing like tat.