First you need to treat the wound. If you are on a hike, then someone may have a first aid kit with everything you need. Take hydrogen peroxide wash the wound. Then treat the tissue around the cut with greenery or iodine. Apply a gasket to the wound and bandage your finger with a sterile bandage.
If the cut happened on the road, then the driver of transport must necessarily have a first aid kit with him. Turn to him, he will provide everything you need.
If you get a wound in the forest, during mushroom picking or on a river where you went out to fish, the situation becomes somewhat more complicated. Treat the wound with what is at your fingertips. It can be carbonated water or even vodka, which you took with you. Then try to gently join the tissues in place of the cut and attach to them the cleanest material that you find in your pockets. It can be a napkin, a handkerchief, toilet paper. Then wind your finger. To do this, in extreme situations, even a piece of a cut shirt or towel, a sock or a fabric belt.
Bandage your finger tightly, but not so tightly that it does not turn blue. Do a few spiral movements along the entire length of the finger, wind more directly over the wound. Then cut the end of the dressing to make the strings. Turn one end in the same direction, and rotate the other one 180 degrees and tie them together.
When you return home, immediately treat the wound with disinfectants and make a bandage with sterile materials.
Take a normal bandage, circle it twice around the wrist, and then bring it to the finger. Then, with the same spiral movements wind the bandage on the finger, overlapping 2/3 each previous turn.
If a severe tumor is found, contact the hospital or the nearest injury center immediately. In no case do not self-cure and do not try to fill the wound with green or iodine. They only contribute to the necrosis of the tissue and slow the healing of the wound.