Hi
Scenario means flow path of the execution.
Ex: Scenario 1:
Login to the yahoomail.
compose a mail N send.
Logout.
Scenario 2:
Login.
Read a mail.
Delete a mail.
Logout.
Similarly you can write a number of scenarios for yahoo mail.
Task means a particular job.
Ex: Login/Reading a mail/Deleting a mail/COmpose.
COmbination of more than one task results in Scenario.
Regards
Sathish