I read the summary about Arduino One (http://arduino.cc/en/Main/ArduinoBoardUno). It's say that I can connect to 12V the arduino input but I want to know if it´s safe to connect directly to a 12v/10A (battery source) with a 12V DC Small Motor and another circuits (all with fusible).
You can connect it up to a 100 Amp source, it will make no difference to the Arduino.
A load (In this case, the Arduino and it's associated inputs and outputs) will only draw as much current as needed.
If you've only ever connected the arduino to the computer's USB 5VDC supply, you will notice when you hook it up to 12VDC that the onboard regulator will get significantly hotter.
One solution to the heat problem is to make a 12V to 5V regulator which is available from Jaycar for under $20.
I will make a regulator.
go to ebay and buy one of those 12 - 5V usb adapters for charging a cell phone. About 3 bucks or so. Keep a couple around the house for other things too. You can easily repurpose these to provide power for most projects.