Helix

From FoldIt Wiki

The helix is one of three basic structure types used in FoldIt. In its ideal form, it appears like a coiled cylindrical spring with all sidechains directed outward. Ideal helices usually have hydrogen bonds between every third amino acid in the chain; this bonding is not visible in the helix representation, but it can be informative to change the helix to sheets to see the hydrogen bond pattern.

The helix structure is used to represent the real protein structure called an alpha helix. An ideal alpha helix will have one coil for every 3.6 amino acids. The closer a particular series of amino acids in your FoldIt puzzle is to that ratio, the more helpful it may be to define it as helix using Structure Mode.