please help about GUID and IMEI!

Hello guys I would like to ask you guys about GUID and IMEI.

1. What is GUID and IMEI?

2. Which one should i change in order to "be different mobile device"

3. if you change mobile device model will IMEI automatically change? or do you have to change it manually?

I got really confused with these because i see GUID, IMEI, mobile device model in bluestacks.

thank you guys in advance!!

To be a another mobile device, you have to change the IMEI. What OS do you use?

Are you using some emulator for this?