[Inziladun]

For a very basic reply, I would say that all creations of Ilúvatar were involved in "subcreation" constantly, as they were continually using and re-arranging things that were already there.

As one descends from the angelic Ainur to the Children of Ilúvatar, the ability to affect the environment becomes less due to the limitations of native power. Elves as the Firstborn generally had more power than Men, with those having spent time in Valinor being greater than the others. Beings like Elrond, with "angelic" blood mad additional leeway, and in his case, his power was augmented by the Ring, Vilya.

Overall, I think the subcreation ability is limited by the amount of one's native power. Men could not learn how to "snow-walk" like an Elf, any more than they could discover the secret of prolonging their lives indefinitely.

And by the way, welcome to the Downs!