Foldings allows collapsing and/or expanding blocks of text logically belonging together. If given language supports such separation (most do), you can use foldings to collapse the text you're not working on at the moment to save space and increase readibility of your code. Editor will automatically find these blocks for you (as defined in specific language grammar). You may collapse the block by click on either the opening or closing arrow icon. Hovering over gray three-dotted icon will display, what's hidden.