Code Folding allows you to hide segments of text in your document, to make it easier to navigate the document's text content. To fold text, first select the text you would like to fold; then, select "Fold Selection" from the Edit menu. When you do this, the selected text will disappear and be replaced by a token:

. You can unfold the text by double-clicking the token or using the "Unfold Selection" command in the Edit menu.
In the "General" section of Latexian's Preferences, you can configure Code Folding to appear in the Gutter. This will show disclosure triangles for folded text segments, which allow them to be unfolded and re-folded. Latexian will also identify Chapters and Sections in your document, and when you move the mouse over the Gutter, Latexian will provide disclosure triangles to fold these segments of text.
Latexian remembers what portions of a document are folded. After you close a document, if you do not modify the document in another editor outside of Latexian, Latexian will restore the code folds that you had previously created.