Bug life cycle starts when a bug is found by a tester. After that a tester has to do several things in different point of times.
The very first things to do before logging a bug is to make sure that this issue has already been identified or not. Simply, searching on bug storing database for similar issue. If bug is already has been entered; make sure it is still active and scenario is same that you have identified. If not reopen it and add more information (if repro. steps are different add your ) and bring this issue to developer's/team's attention.
Always avoid entering duplicate bug. Adding duplicate bug effects a tester image .
After tester entering a bug it must be assigned to someone, mostly to developer. (Eventually goes to developer). Developer checks bug and then fixes his code in same build, produces a new build with fix and assign bus to tester to verify it. Now tester needs to verify the fix, which is called regression testing. If bug has been fixed, it is tester's responsibility to close it. If not, the bug will be reactivated and cycle will starts all over again.