To get a random number in Excel, use the
RAND() function, which returns a random number between 0 and 1. It will return a different random number each time the cell is recalculated, such as when you reopen the workbook (e.g. press F9 to refresh and you'll see the value change).
Random Numbers In a Specified Range
To get a random integer (i.e. whole number) in a particular interval, use the
RANDBETWEEN() function, which has two inputs noting the lowest and highest values you want random numbers between. E.g.
=RANDBETWEEN(200,300) will return a random integer between 200 and 300. Again you'll get a new random number each time you refresh (you can Copy and Paste Values if you want to keep the random numbers you've generated).
If you need a random number in an interval which isn't rounded to the nearest whole number, you can use the RAND() function output to do get this. For example,
=200 + RAND() * (300-200) will give you a random number between 200 and 300 which isn't rounded.
The output from each of these functions is shown in the below output: