The subject of a sentence is the person or thing which does an action.
I wrote the report.
We carried out the experiment.
The group analysed the data.
The subjects used can indicate how personal or objective a piece of writing is. Some tasks, such as reflective writing, encourage you to use 'I' and put yourself and your experience at the heart of your writing. Other tasks, such as reports, require a more distanced, objective style. In this case, the subject is often less personal:
The project involved a number of different stages.
The results indicate that more work needs to be done in this area.
Click on the subject in each of the following sentences.