A good way to master the content of a text is to summarize it: reduce it to its main points, in your own words. Some assignments call for brief summaries, as when you summarize the plot in a critical essay about a novel. Summary, however, is also an essential tool in research papers and other writing that draws on sources.
A summary should state in as few words as possible the main ideas of a passage. When you need to summarize a few paragraphs or a brief article, your summary should not exceed one-fifth the length of the original. For longer works, such as chapters of books or whole books, your summary should ne quite a bit shorter in proportion to the original. Below you can find a procedure for drafting a summary.
Here you can find an excerpt from a J. Gee paper on videogames.
The first step towards understanding how videogames can (and we argue, will) transform education is changing the widely shared perspective that games are "mere entertainment." More than a multi-billion dollar industry, more than a compelling toy for both children and adults, more than a route to computer literacy, video games are important because they let people participate in new worlds. They let players think, talk, and act-they let players inhabit-roles otherwise inaccessible to them. A 16 year old in Korea playing Lineage can become an international financier, trading raw materials, buying and selling goods in different parts of the virtual world, and speculating on currencies. A Deus Ex player can experience life as a government special agent, where the lines between state-sponsored violence and terrorism are called into question.
This is a textbook example of an introduction. The topic sentence comes first, stating that videogames will change education because they are more than just entertainment. As is usual in paragraphs that have the topic sentence at the beginning, the move goes from general to specific: the first part of the second sentence is already at the same time an more detailed elaboration of the topic ("it's also about industry & computer literacy"). At the end of the second sentence, new information is added: videogames let people participate in new worlds. Also note the comparative way in which Gee, in this second sentence, presents his arguments: in doing so, he not only creates a (mini-)climax, but also successfully captures his readers' attention. The theory is then illustrated with 2 examples.
Videogames are more than just videogames: they are profoundly changing the world we live in, affecting not only industry but also education. In games like Lineage or Deux Ex, players can enact different roles in videogames and experience new worlds.
This is not a bad attempt, albeit perhaps somewhat too long; the reference to examples is not quite necessary; there's also no mention of the impact videogames have on computer literacy.
Next to their huge impact on industry and computer literacy, videogames will change our educational system because they allow for role playing.
This is better: short, yet capturing the essence of the original paragraph.