Buttercup squash has a dark green skin and is a relatively dark orange flesh. The outside can look almost similar to acorn squash, but the inside color is more like butternut. The texture and flavor is relatively similar to butternut too - it has that same smooth texture and isn't stringy.
These big plants need lots of food. Use 1 cup of complete organic fertilizer worked into the soil beneath each plant. All squash grow male flowers first, at later female flowers. The female flowers have tiny fruits at the base of their petals and require pollination by bees mostly. Incomplete pollination often happens at the beginning of the season, and results in misshapen fruits that are withered at the blossom end. Just discard these damaged fruits before they begin to rot. Encourage bees to visit the garden by growing Phacelia, sunflowers, or buckwheat for improved pollination.
Pick when small, if fruit gets big the plant stops producing. Check the plants regularly.