What is the general structure method for writing in the style of a report?

There is no actual real definitive answer; for example, some people may choose to exclude an introduction and include an executive summary instead. The important thing is to check with whoever is marking it! However, if nothing is provided, the following is what I would generally recommend:

1. Abstract / 2. Introduction / 3. Methodology / 4. Results / 5. Discussion / 6. Further work / 7. Conclusion / 8. Appendix

This is by no means the only way you can write a report, but this structure would provide safe grounds for a decent mark, provided you are not doing something against instructions.