Best Of

You can actually achieve a flat spiral with the helix tool without needing the edit curve step if you use the axis mode and draw to an end point. I was messing around with opHelix when writing some curve features and it supports flat planar outputs as well as cylindrical / conical outputs. Weirdly though it doesn't support cylindrical AND flat outputs simultaneously (i.e. a flat circular arc output) so I had to write my own 3d circular arc functions to compensate.

You'll have better luck getting help if you provide the info (text, pics, description of what specifically is hanging you up) rather than asking for people to go on a scavenger hunt. By asking in the way that you have you have limited your audience to those in the "know" and those that are curious and have plenty of time to research. Is this what you want to model?

One of the multiple ways:

Helix curve then use Edit curve to planarize and reapproximate (smooth)

https://cad.onshape.com/documents/8efddfb1d2b9f0efb133f1da/w/852a25bd82baf51214f78c61/e/1c8417d1d56c4bb11da2ddba

there are multiple ways:
us a featurescript (by @Pascoe):
https://cad.onshape.com/documents/abb998532f54a132a42bea8b/v/c8a10bd7be466c936ab1e590/e/fd1c85d2bd07ba022788d886

or create a helix on a cone. (and if you need a flat spiral, you can project it onto a plane)