To generate random numbers (integers) between two numbers, you can use

=RANDBETWEEN(x,y)

where x and y are your lower and upper limits. You can then fill this formula down and across as many rows/columns as you need.

Note, however, that RANDBETWEEN is a volatile function. This means that anytime the spreadsheet changes or recalculates, those numbers will change. To avoid them changing after you've gotten the random data, select all of those cells and choose Copy, then click Edit-PasteSpecial-Values. This will over-write all of those cells with their values, removing the RANDBETWEEN formula.