When one number will divide exactly into the other one then the other one will be the LCM. For example the LCM of 4 and 8 = 8 .
When they do not divide as above then the product of the numbers may be the LCM. For example the LCM of 3 and 4 = 3*4 = 12.
The product is not always the LCM. It might be a lower number . For example the LCM of 4 and 6 is not 24 but 12. ( 24 / 2).