Welcome to permies.
LEAVES: They are natures way of returning nutrients to the soil. They also feed
the soil 'critters'.
In a natural forest, does anybody rake up the leaves?
I would say that they can be left, as is, in the garden beds
. On a lawn, they will do little to help. Perhaps you can rake the lawn, and leave the pile of leaves to break down over the winter, and into spring. They can then be used as a mulch/compost, anywhere that you wish.
In a pond, the nutrients will settle to the bottom, adding much life for flora/fauna.
COMPOST: Can either be spread on the garden soil, and/or turned into the soil.
Decayed organic matter is the primary source of food for much of your 'Soil Food Web
It is what turns dirt into soil. It improves water
holding capacity to the soil. It helps avoid compaction of the soil.
The SFW will continue consuming it, exuding more life into the soil.
PLANTS: If they are perennial plants, just leave them be. They should
spring back into life in the warming days of spring.
Annual plants could be chopped off at ground level, leaving the roots
untouched within the soil. The roots worked hard to infiltrate your soil, and as they decay, they will feed the SFW, and leave tunnels for air and water to infiltrate deeper into your soil. This will allow the next generation to drive deeper into your soil next spring. Each generation (up to a point) should be able to grow more and deeper roots, thus extending the depth and tilth of your topsoil.
CAVEAT: If any plants are diseased, they should be removed (roots and all). Some people
compost them, but this can lead to returning the disease to your soil. Most people recommend burning
diseased plants, as this should assures that you are not reintroducing the disease to the next generation.
Wander around this site, as there is an abundance of useful knowledge here, and the natives are friendly