Whether you can print or copy part of the book depends on the type of document you are trying to print or copy.
If you are trying to print or copy a document provided by your instructor, then your instructor determines whether the document may be copied or printed. If you don't see the option to print or copy (see below), contact your instructor.
If you are trying to print or copy a book that you purchased through Perusall, you may or may not be able to print or copy the book, depending on the publisher's rules. Note that even if enabled, the amount of the book that you may print or copy is limited, so only print or copy as much as you need.
If printing is allowed for a particular document, you'll see the print icon in the toolbar and can select a range of pages or sections to print:
If copying is allowed for a document, the Copy to clipboard option will appear in the toolbar when highlighting text: