Hi
If your actual behaviour of the application is something which is different from what is expected follow the below steps.
1) Verify if your testcases are as per the requirement.
2) Verify if valid testdata is being used.
3) Try to replicate it with n number of possible combinations of testdata.
4) Take snapshots of the screens where you found the deviation.
5) Communicate to Developer about the Deviation found and finalize whether it is a defect.
6) If you are sure it is a defect at a first go log in the defect tracking tool with proper severity and priority details. Also steps to reproduce should be very much precise so that a lay man should also be able to reproduce that defect by following the steps.
7) Attach the snapshots for reference purpose for Development team.
Please write to me @ sukanya.kambhampati@gmail.com incase you need any additional information.
Regards
Sukanya