The simplest (and possibly least efficient) way to
test a number for being prime is to divide it by every number less than itself. if any return a 0 remainder, the number is not prime.
I'd suggest starting off writing that code. pick a number, say 91. write a loop that tests the remainder for every possible number from 2 to 90. set a boolean before you start, something like isPrime = true;. then, if you ever get a 0 remainder, set it to false.
after you check all the possible numbers, and exit the loop, use your boolean for printing prime/not prime.
I'd put all that code into a method.
Then, change the method so that instead of being hard-coded to testing 91, you can pass it a value to test. Write your main to pass it 91, then call it again with 17 then again with 48.
Then, write a loop that would call that method, passing in the values from 2 to 100 (or whatever).
Note that once you have it working, you can start tweaking the method that checks for primality without effecting anything else. Keep the original copy of the method, and make a primeCheck2() method. tweak that one - maybe you only need to check to up to 1/2 the original number. or maybe only up to the sqaure root.
maybe you could keep a list of the primes you've found, and only divide by those...
the point is that you want to separate out the different parts of your code. the prime-checking part should be completly separated from the "which number to check" part. which should be separate from the "get input from user and validate it" part...
These are some ideas to consider when writing your program.