Are you looking to get changes made to the Android software and you own a Samsung device? You will need the smartphone or tablet booted into the Download Mode before you can do that. If it is flashing that you need to be done from the Odin flashing tool—whether it be flashing a custom recovery, rooting files like Chainfire’s CF-Auto-Root or just a stock ROM—the device must be in Download Mode before it works. The Download Mode for Samsung is what the Bootloader Mode is to numerous other OEMs and manufacturers.
The Download Mode for all Samsung devices is a universal mode that is accessed by pressing the same hardware button combination. Rooted users can install an app like Quick Boot  that helps boot into the various available modes for a smartphone or tablet, but regular Android users who are unrooted need to get into the Download Mode using the button combination that can be found on the device. The only exception to that is if you want to run some ADB commands from a computer.
Using ADB is a bit of an outlandish idea just for getting into Download Mode in the same way that most people don’t use ADB for taking complete backups although hit is possible to do. There is nothing you can’t do from Android Debug Bridge, and you can follow our step-by-step guide for setting it up  if you want to give it a go. For everyone else, we recommend using the hardware button combination to get Samsung devices into the Download Mode, and the guide below shows you how that is done.
HOW TO ENTER DOWNLOAD MODE ON SAMSUNG DEVICES
- Start by turning off the smartphone or tablet.
- Boot it up by holding the Power + Home + Volume Down keys at the same time and keep holding them.
- Release the keys when the screen turns on and greets you with a warning message. (The message on the display lets you know that installing a custom OS can cause critical problems for the phone or tablet and its applications).
- Press the Volume Up key to get the Samsung smartphone or tablet into the Download Mode. (Those who want to go back can do so by pressing the Volume Down key instead).
- Once you press the Volume Up key, the smartphone or tablet will show a downloading target screen. That screen will stay on the device until you flash whatever it is that you are flashing.
In conclusion, that is how to enter Download Mode on Samsung smartphones and tablets using the hardware button combination.