The Samsung Galaxy J5, released in April 2016, is one of the flagship Samsung phone in Europe, India is less popular in the United States (it can be used in North America, only it's mostly sold elsewhere).
Probably a marketing strategy to not interfer with the current S7.
Like many of the other Galaxy devices, it does typically come connected to one mobile carrier. If you've picked up the J5 and want to use it with a different network, or in a different country all together, you first need to unlock the Galaxy J5.
Thankfully, that isn't all that hard to do.
Locate your J5 IMEI number
This is a special number to your phone. With the Galaxy J5 using a metal backing and a higher-end, premium design, you most likely are not going to obtain the number by removing the battery.
Instead, power on the phone and type in *#06#. After you enter this into the keypad it automatically shows you the IMEI number. Write this down, because you'll need it later.
Obtain your Samsung network unlock code
Unlocking mobile phones is far easier to do now than it was a few years ago. Back then, if you purchased a phone and wanted to unlock it, you had to go deep into the operating system and make direct alterations to how it functioned.
This often prevented the phone from updating, it rendered the warranty useless and it caused all sorts of problems further on down the road. With your IMEI, you just need to head over to the SIMlock website and enter in this IMEI number.
Once you do, you can receive your Samsung unlock code.
Finish unlocking the phone
Now that you have the unlock code, you are ready to unlock your Galaxy J5. Remove the SIM card from your device.
Make sure to store it carefully as, due to the size, it is easy to misplace it. Slide the new SIM card from the non-supported mobile carrier into the device.
After a moment, a notification window will pop up stating "SIM Network Unlock PIN." When this appears, type in the unlock code you received from the SIMlock remote unlocking service.
Upon entering the code the phone will take a moment to process it. Upon completion, it recognizes the new SIM card and allows you to use the device on the new network.