Animals can be classified in many ways; We can classify them according to their diet (carnivores, herbivores, etc.), according to their habitat (terrestrial, aquatic, flying), according to their type (vertebrates or invertebrates), according to their group (mammals, birds, reptiles, among others).
The important thing about all this is that everyone has a role to play within the dynamics of the planet, from the largest (such as whales or elephants), to the smallest (such as ants or bees). Although it is true, the vast majority of us do not have any kind of contact with non-domesticated fauna; for that reason, we can't do much for it. Our "hands are tied" and we have neither voice nor vote to prevent the atrocities, damages and contamination suffered by forests, jungles, oceans... and their respective fauna..
However, if we can help the animals that are in our environment: dogs, cats, birds, some reptiles and insects.
For example, if we see a homeless animal (puppy or kitten) on the street and we have the chance to offer it something to eat or drink... let's do it; We will feel unmatched happiness and inner peace, I guarantee it =)
In addition, it is very likely that the little animal spends hours or days looking for water or food, looking for help; and by finding a helping hand, by bumping into us, he will undoubtedly feel very happy, or at least it will calm his pain and his sorrows for a brief period of time.
After having carried out this action, the best thing to do would be to report the animal (and its respective location) to the rescue groups and shelters in the area, through social networks.
We can also help the birds, placing drinkers so they can hydrate in the summer months (in which it is very difficult to find water). If we live in a building, we can place a drinker and some fruit outside the window to feed the birds; If we live in a house with a garden, and we have fruit trees, let us always leave some ripe fruits on the tree, so that the birds that are passing through can feed.
Even insects we can (somehow) help. If we see a bee without much strength and disoriented, we can offer it a drop of water (sometimes it works); Normally, when we find them in that state, it is a product of dehydration, and this saves their lives.
If we observe an ant, a butterfly (or another insect) drowning in a puddle or in a container with water; let's take it out and put it in a dry place. For us, it means nothing (it takes only a few seconds), but for them it means life.
In short, if we do not have resources to greatly help the rescuers and the different shelters (and to help preserve the fauna), we can also help in the way mentioned above, it is also valid. :)