Hi,
I have an Arduino UNO and 2 devices that needs to be attached in it both are 12v. The first device is already connected on VIN & GND but I need to connect another one can I just solder them together like connecting the VIN of the the 2 devices plug it on my arduino? Sorry I'm really new to this hardware stuffs 
Yes.
Do you mean VIN on the power header, or are you calling the barrel jack connector VIN?
The power header is after the reverse polarity protection diode, that diode has a 1 amp limit.
If you connect before going into the barrel jack there is no limit.
I have an Arduino UNO and 2 devices ...
It would help to be more specific about these devices. What are they? Motors? Lights? Relays? And some technical specs would help.
CrossRoads:
Yes.Do you mean VIN on the power header, or are you calling the barrel jack connector VIN?
The power header is after the reverse polarity protection diode, that diode has a 1 amp limit.
If you connect before going into the barrel jack there is no limit.
I'm not really very familiar with technical stuffs but I'll try to use your suggestion. Thanks for your reply
Sorry sir this device
http://www.e-gizmo.com/KIT/e-TERM.html
http://www.e-gizmo.com/KIT/images/eterm/E-term.pdf
the other one is a Digital Comparable Electric Coin Selector can't find technical info for this device