While the artifacts are the heart of your portfolio, you also need to describe and analyze them in writing to ensure your readers understand what these artifacts are and what they reveal about your knowledge, abilities, motivations, and identities.
You should compose a separate statement for each portfolio artifact. In short, this text guides your reader in how to read and how to understand each artifact. You should have an absolute minimum of two paragraphs for each of your five artifacts: the first paragraph briefly explains what this artifact is and describes the context within which you created it, while the second paragraph (and possibly more) analyzes what this artifact reveals about what you know or know how to do.
How much framing discourse you include should serve the reader and should help you achieve your purposes for your portfolio; in other words, what specifically you say about each artifact is a rhetorical decision, which will vary from individual to individual.