Citing sources correctly is essential in academic writing for several reasons:
Quoting means citing the author verbatim, that is to say, without changing anything in the text. Any minor change in the text must be put inside square brackets [...]. If you omit a part of the text (ellipse), it must also be indicated by three dots inside square brackets [...], and the ellipse should not change the meaning of the text. If you decide to underline a part of the citation or put some words in bold or italic letters, it should also be indicated ("emphasis by author"). And of course, the citation itself must be put in inverted commas.
Paraphrasing means restating the ideas of someone else in your own words. It does not mean just replacing a few words with synonyms. It is generally recommended to change the structure of the text. Of course, the author and the source must be correctly referenced.
It can be difficult to know whether a paraphrase is too close to the original text or not. This short video gives an example of good paraphrasing.
To summarize, you must shorten the original text, keeping the main points only , in your own words, and, of course, the source must be correctly referenced, and the author's thought not misrepresented.
Whether you quote, summarise or paraphrase, you must always cite the source, giving all the necessary metadata. And you must, of course, take care not to misrepresent the author's argument.