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Fibermesh-Micromesh and Transparent 3d Plane and Background

Fibermesh-Micromesh and Transparent 3d Plane and Background.
Using for an example the tree tut and the new presets tut for fibermesh and micromesh i have a couple of questions.
How do I turn the background (in new presets tut it’s blue) into transparent. How do I turn the 3d plane (in the tree tuts) transparent.
I would like to save just the tree or the grass or the grass with weeds image once it have been rendered.
Step by step please or a vid.
Thanks

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