The question needs clarifying, so I'll place it into two answers for the two possibilities.
If in question to white spots on the nail itself, this is often due to the nail being damaged whilst in the process of being formed inside the finger. So if one were to, for example, smash their thumb in a door, the results would not only be a bruised thumb but when the nail grows out you will see a white patch where the formation of the nail was interrupted by the impact of the door.
Some people often wonder if it's due to a deficiency of some sort of vitamin or the like, which is one of the least likely causes. Such a deficiency, however, may cause the nail as a whole to become more brittle or softer, whatever the case may be, and thus more susceptible to becoming damaged.
Now, if it was in question to a bruise beneath the nail, it's no different than a bruise on the skin. Whatever impact or incident brought about the bruise remained, for the most part, internal and so blood escapes the vessels beneath the skin or nail and shows through the thin layer. The color of the bruise depends of whether the escaping blood is oxidized or not, blue blood being the non-oxidized.
(This is all a wild guess from personal knowledge and experience. I didn't do any research, so feel free to correct me.)
Your toenail is too long and the shock it receives from your shoe when you walk can actually tear the toenail in places from your toe. Trim your nail and it will recover.
Fungi is caused when you get water stuck underneath your toenail which causes a type of mold.
A lot of things could cause that but most likely some sort of impact.
underneath a toenail or fingernail (black toenail)
If the toenail is too long or if it is dry, then it will split.
NOT mustard powder ! CORNSTARCH !... Cornstarch acts as a coagulant to slow down bleeding.
It will start bleeding...
The erosion of the esophagus is what causes the bleeding when you purge.
An ingrown nail will cause that problem.
Information about Bleeding Diathesis can be found on the wikipedia article which has reliable information and the causes. Some of the causes for bleeding diathesis are excessive bleeding and a lack of clotting.
The fungus is underneath the nail, so nothing you paint on top of the nail really helps unless it is a prescription medication specially designed for that. See your doctor to decide what medicine you need for your toenail.
Bleeding occurring outside the body.
No it is most likely a bruise caused by trauma to the toe. The dark color is from bleeding under the skin.