Why is char *A able to hold strings while char A cannot?

Char pointers are assumed to point to the beginning of a string.
The pointer itself points to the first character in the string, and code using the pointer assumes that the rest of the string follows it in memory, until it reaches a \0.

Picture:

+---+---+---+----+------
| A | B | C | \0 | ???
+---+---+---+----+------
  ^
  |---char*

Yes, each char* can point to only a single char at a time. But C++ strings like "ABC" are stored in memory as a contiguous sequence, without holes and with a 0 char at the end. Therefore, if you have the pointer to 'A', ++pointer will get you the pointer to 'B'. And you also know that you can do ++ until you find that last '\0'. (Which is exactly what strlen("ABC") does - use ++ 3 times to find the 0, so it returns 3.)