Look at your keyboard. You'll notice a collection of letters - top row starts qwert. Next row down is asdfg.
Start at the A. Directly to the left of the A you'll see a key marked "Caps Lock".
On most keyboards, when this button is depressed there will be a light that indicates that it is on.
While this button is down, all the letters you type will come out in capital letters. So for example, hello would read as HELLO.
Generally, no one will read a post that contains all capital letters, except maybe to respond with instructions on how to use the caps lock key.
Hopefully you have found this both informative and helpful.