The division operator / divides the numerator by the denominator, generating an error in the case of a division by zero. However, the error does not stop the calculation, but it can be intercepted by ISERROR and IFERROR functions. If the error is not intercepted, the division returns positive or negative infinity depending on the sign of the numerator, or NaN in case of 0 / 0.
The DIVIDE function provides an alternate result in the case of a division by zero and does not raise an error that could be intercepted by ISERROR and IFERROR.
Any argument passed as a string is automatically converted into a number.
The following two expressions return the same result.

20 / 4
"20" / "4"

Boolean values are converted into numbers (0 for FALSE and 1 for TRUE) when they are involved in a division.
Read BLANK handling in DAX for a complete description of the effect of BLANK with different operators.