The poem opens with an offering: “Glory be to God for dappled things.” In the next five lines, Hopkins elaborates with examples of what things he means to include under this rubric of “dappled.” He includes the mottled white and blue colors of the sky, the “brinded” (brindled or streaked) hide of a cow, and the patches of contrasting color on a trout. The chestnuts offer a slightly more complex image: When they fall they open to reveal the meaty interior normally concealed by the hard shell; they are compared to the coals in a fire, black on the outside and glowing within. The wings of finches are multicolored, as is a patchwork of farmland in which sections look different according to whether they are planted and green, fallow, or freshly plowed. The final example is of the “trades” and activities of man, with their rich diversity of materials and equipment.

Fresh-firecoal chestnut-falls; finches' wings;

And here come two more hyphenated words, along with two more examples of "dappled things." The first example is "Fresh-firecoal chestnut-falls."
This is probably the trickiest image in the poem, partly because we're not nearly as familiar with chestnuts as 19th-century English people would have been.
"Chestnut-falls" is not too hard to imagine. It refers to chestnuts that have fallen off the chestnut tree. This hyphenated word points to the specific chestnuts that have fallen from the tree.
But "Fresh-firecoal" requires some background on nuts, a field we at Shmoop like to call nut-ology.
When they are on a tree, chestnuts are covered by a spiky, light-green covering, but the nuts themselves are reddish-brown.
When the nuts fall, they are "fresh" from the tree. Because of the contrast of red nuts with their outer covering, they look like the burning of coals inside a fire.
To add another layer to this chestnut conundrum, people also like to cook these delectable nuts over fire. When the nuts get hot, they open up to reveal their "meat," inside. These opened chestnuts also look like embers.
We're almost certain you now know more than you ever wanted to about chestnuts. Fortunately, the second example of a "dappled thing" in this line is much easier.
Finches are small birds with streaks and spots.
The speaker focuses only on the finches' wings – a sign of his great attention to detail.