A paraphrase restates a short passage and can be as long or longer than the original passage. A summary restates or highlights the writer’s main point(s) and is much briefer than the original material.
Whether you use a paraphrase or a summary, you need to completely understand an idea before attempting to put in into your own words. Otherwise you could misrepresent what the source is saying. OR your paraphrase or summary could end up echoing or resembling too closely the wording and sentence structure of the original material -- which is plagiarizing, even if you cite your source.