Q:

Syntax for creating a two-dimensional array

Consider:
int[][] multD = new int[5][];
multD[0] = new int[10];

Is this how you create a two-dimensional array with 5 rows and 10 columns?
I saw this code online, but the syntax didn't make sense.

A:

Try the following:
int[][] multi = new int[5][10];

... which is a short hand for something like this:
int[][] multi = new int[5][];
multi[0] = new int[10];
multi[1] = new int[10];
multi[2] = new int[10];
multi[3] = new int[10];
multi[4] = new int[10];

Note that every element will be initialized to the default value for int, 0, so the above are also equivalent to:
int[][] multi = new int[][]{
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }
};

A:

We can declare a two dimensional array and directly store elements at the time of its declaration as:
int marks[][]={{50,60,55,67,70},{62,65,70,70,81},{72,66,77,80,69}};

Here int represents integer type elements stored into the array and the array name is 'marks'. int is the datatype for all the elements represented inside the "{" and "}" braces because an array is a collection of elements having the same data type. 
Coming back to our statement written above: each row of elements should be written inside the curly braces. The rows and the elements in each row should be separated by a commas.
Now observe the statement: you can get there are 3 rows and 5 columns, so the JVM creates 3 * 5 = 15 blocks of memory. These blocks can be individually referred ta as:
marks[0][0]  marks[0][1]  marks[0][2]  marks[0][3]  marks[0][4]
marks[1][0]  marks[1][1]  marks[1][2]  marks[1][3]  marks[1][4]
marks[2][0]  marks[2][1]  marks[2][2]  marks[2][3]  marks[2][4]

NOTE:
If you want to store n elements then the array index starts from zero and ends at n-1.
Another way of creating a two dimensional array is by declaring the array first and then allotting memory for it by using new operator.
int marks[][];           // declare marks array
marks = new int[3][5];   // allocate memory for storing 15 elements

By combining the above two we can write:
int marks[][] = new int[3][5];

A:

You can create them just the way others have mentioned. One more point to add: You can even create a skewed two-dimensional array with each row, not necessarily having the same number of collumns, like this:
int array[][] = new int[3][];
array[0] = new int[3];
array[1] = new int[2];
array[2] = new int[5];

