A lab report is an account of an experiment and what was discovered. There are three main purposes of a lab report: to communicate exactly what occurred in an experiment by presenting data, discussing the results, and providing conclusions.
It should be written so that: someone else could read the report and understand exactly what you did; someone could read the report and repeat the experiment and get the same results; and, someone could read the abstract and decide whether to take the time to read the full report.
The typical components of a lab report are the following:
As the requirements may vary for your course, always check with your professor!