They gain energy by eating food.
From the food they eat.
In the context of an energy pyramid, between foxes, grasshoppers, birds, and grass, foxes have the smallest number of organisms. There are 21 species of foxes.
It gives energy to foxes and other animals
No, objects that gain energy become hotter.
Volcanoes gain energy from the hot magma inside it
When condensation occurs, it is a gain thermal energy.
You gain Potential Energy as you cycle up a hill.
A temperature change requires as gain or loss of heat energy.
Most substances lose or gain energy when their temperature changes.
Sure, you can add energy to an object. For example, you can heat an object up (to have it gain heat energy), you can raise it (to have it gain gravitational potential energy), or you can make it move (to have it gain kinetic energy). In each case, the energy has to come from somewhere.
Lose
you can gain energy by absorbing sunlight or having an energy drink, having a good nights sleep, going to bed early.