There are already tooltips with short explanations, but there's only so much space and I wanted to share a few tips as well.  So here they are!

• Spline Resolution: Resolution of the curve on the vertical direction.
  
  • Extremely low values may make even 2a and 4c hair indistinguishable. Try to balance legibility and performance!
• Bevel Object: External curve object used to add a custom bevel shape to the curves. MUST be a cyclic curve.
• Bevel Resolution: Resolution of the bevel object.
  • As a rule of thumb, you should keep this way lower than the Spline Resolution.
• Fill Caps: Whether or not to fill the end caps.
  • This is only really necessary if the endpoints aren't scaled to 0.
• Radius (mm): Multiplies the radius of every end point, in millimeters.
  • This doesn't mean the radius of every point is the same. Use Alt-S in Edit Mode to shrink or fatten individual points.
• Material: The material of the curves.
  • If you don't know what a material is, you need to look into beginner tutorials for Blender as a whole. Take your time.
• Curl: Frequency of the curling, based on real world curl scale. 2.333 is 2b, 3.667 is 3c, etc.
• Bevel Offset X/Y: Offsets the bevel object in order to make the curls more obvious.
  • This can also be done manually in Edit Mode, if you prefer.
• Bevel Rotate: Rotates the bevel object, in order to fix thinning issues caused by higher curve scale.
  • You might want to look at the Face Orientation to make sure the normals are facing outwards, as inwards normals can cause shading issues.
• Random Floof: Randomizes the position towards the endpoints. Starting points have little to no randomization.
  • This means that the "direction" of each curve matters here. If there's no randomness at the ends, go to Edit Mode and with the whole curve selected, click on the Segments menu and click Switch Direction.
• Floof Seed: Seed for randomization.
• Floof Scale: Scales the noise texture used to offset the curves. Might look noisy or bad at high values.
• UV: Name of the generated UV Map used for material textures. Recommended name is "UVMap."
  • Use an Attribute node with the same name in your material instead of using the texture coordinate node.
  • This is not a substitution for UV unwrapping, as it is a generated attribute.