A much better introduction to the area in which I worked than I could provide can be found at the site of The Particle Adventure.
Within particle physics, what I did is described as “particle phenomenology” that is, the study of things that happen in particle physics experiments. This might be simply described as looking at different theories to determine what they predict we ought to see in experiments, and then comparing this with experimental data to see whether a theory is actually right. Of course, this is a gross oversimplification, and both making predictions and looking at data are hard things to do!
The kind of experiments needed to get the kind of information in which I'm interested are themselves huge endeavours, and result from collaborations of thousands of people. An example of such an experiment is the Large Hadron Collider at CERN, about which the UK physics community has a website.
My recent work has been in extra dimensional phenomenology (particularly of the ADD model) in the electroweak sector: see my publications page.