You can enter numbers and symbols either by clicking them with the mouse or by typing them at the keyboard. For example, to have Calculator compute the sum of two and two, you could:
Or you could type:
2+2=
Try experimenting with both methods to see what works best for you.
If you're adept at typing numbers, you'll probably find it quicker to enter numbers at the keyboard. To get the result of a calculation, you can press either the Enter key or =. You'll find the mouse convenient for entering such things as sqrt and 1/x. If you prefer to use the keyboard all the time, you can do so; the Calculator buttons all have keyboard equivalents. (Online help includes a handy table of keyboard equivalents.)
Calculator normally displays large numbers as a simple string of digits. You can make the display more readable by choosing Digit Grouping from the View menu. This breaks up large numbers with commas when you use the decimal number system or spaces when you use the hexadecimal number system.
Calculator can exchange numbers with other programs by way of the Windows Clipboard. If you choose the Copy command (on the Edit menu) in Calculator, whatever number Calculator is currently displaying is transferred to the Clipboard. If you choose the Edit menu's Paste command while in Calculator, the current contents of the Clipboard are transferred into Calculator character by character, as if you typed the characters at the keyboard.