star = 1;
while ( star <= numStars  )
{
  System.out.print("*");
  star = star + 1;
}

Fitting the Two Pieces Together

So.... now you have two pieces: (1) the part that ensures that the required number of lines "happen," and, (2) the part that prints the required number of stars per line. Here is a complete program, the two parts fitted together:

import java.io.*;
// User picks ending value for time, t.
// The program calculates and prints the distance the brick has fallen for each t.
//
class starBlock
{
  public static void main (String[] args ) throws IOException
  {
    int numRows;      // the number of Rows
    int numStars;     // the number of stars per row
    int row ;         // current row number
    int star;         // the number of stars in this row so far

    BufferedReader userin = new BufferedReader (new InputStreamReader(System.in));
    String inputData;

    // collect input data from user
    System.out.println( "How many Rows?" );
    inputData = userin.readLine();
    numRows   = Integer.parseInt( inputData );

    System.out.println( "How many Stars per Row?" );
    inputData = userin.readLine();
    numStars  = Integer.parseInt( inputData );

    row  =  1;
    while ( row <= numRows )    
    {
      star = 1;
      while ( star <= numStars )
      {
        System.out.print("*");
        star = star + 1;
      }

      System.out.println();         // need to do this to end each line
      row = row + 1;
    }
  }
}

The part concerned with printing the right number of stars per line is in blue. Notice how one while loop is in the body of the other loop. This is an example of nested loops. The loop that is in the body of the other is called the inner loop. The other is called the outer loop.