Greetings, Gary :)
So, I was always told that an essay usually had to contain more than three paragraphs, whereas a summary had to be at least three sentences.
So, when writing a summary, you would not use the same rules as writing an essay, but they'd be pretty similar. In summary's and essays, you have to put down complete ideas and sentences, as well as having correct grammar.
For an essay, you have to write an introduction, body, and a conclusion, but for a summary, all you would have to do is write what the general idea is.
*Remember to always use correct punctuation, because most professors and teachers take off points if they see incorrect spelling.
~Hope I helped!~