What is the ecological group of cervidae, cestoda, and euphorbia? What is their relationship to humans?

First of all, what are these organisms? These Latin names may be unfamiliar.

Cervidae are more commonly known as deer.

Cestoda are a genus of flatworms which includes tapeworms.

Euphorbia are a large genus of flowering plants called spurges. The one you're probably most familiar with is poinsettia.

Deer are herbivores; they are near the bottom of the food chain and get their energy directly from plants, which get it from the sun. This makes them ecologically consumers. As far as their relation to humans, we mostly consider them a nuisance, but many people kill them for food (acting in one of our many ecological roles as a predator, which is another type of consumer).

Cestoda are parasites; they live inside other organisms, chiefly other animals, and skim off resources from their hosts. This makes them also consumers. Some, such as the beef tapeworm, can infect humans, usually via the animals we eat.

Euphorbia on the other hand are photosynthetic, like most plants. They depend upon animals for their pollination (that is what flowers are for), but they get their energy from the soil and the sun. This makes them ecologically producers. While humans depend on many flowering plants for food (particularly fruit), most of the plants we tend to eat aren't Euphorbia specifically. There are a few herbs in this genus, as well as some decorative plants such as poinsettia, but not much in terms of plants we would regularly consume, likely because Euphorbia typically produce latex, a milky, irritating sap. (Not to be confused with rubber latex, which is produced by rubber trees, which are actually Ficus and not Euphorbia.)