1) Press and hold on an empty space on your homescreen, which should prompt a menu to appear at the bottom of your screen (though it may be slightly different depending on which phone you're using)
2) Select "Widgets" from that popup menu
3) Scroll through the list of widgets until you find the one you want to add
4) Press and hold it, then drag it to the homescreen of your choice
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You'll need a widget for that. Some phones may have one built in, and you can find many on the Play store. I personally use this one, which has tons of customizable options.
To use a widget, long press the home screen an you should have some options pop up, including widgets. You have to use that to activate and place them, as they will not show up in your app drawer like a normal app.