Hi Mar_,
Have a look here,
https://store.arduino.cc/usa/arduino-uno-rev3
Go to the DOCUMENTATION tab down the page for a lot of info about the UNO. Especially the bit on POWER.
Here,
https://store.arduino.cc/usa/arduino/entry-level
Shows you some of the Arduinos.
Not by any means the be all and end all but it is a good place to start.
Daz