There are 2 ways to add a point guide to a sheet.
1.The first and easiest is to hold down the left mouse button on the ruler origin in the upper left hand corner of the rulers (If rulers are visible) and drag it into position.
2.The second method is to click on the 
button in the Add→Guides button group.
3.
The point guide and its X,Y position during initial creation
In both cases, as you drag the guide to position it you can enter a number value by first pressing the Enter key and then the X and Y coordinate or click the left mouse button to place the guide.
You can press the 's' key at any time to turn snap on or off.