What is the maximum current for each I/O pin?
This comes up as first result when Googling your question:



And can be confirmed by page 313 and 314 of the datasheet:



To know where each pin is connected to (on the Arduino Uno) you can look the official (messy) schematic.

I provide an excerpt below that shows the Vin and 5V pins at the headers, and the power barrel connection. 



If you want to control a 12V motor or a 12V LED strip or other DC loads you can use the following (which is also easy to find using Google):

*Note that your 12V Gnd and Arduino Gnd have to be connected.







simulate this circuit &ndash; Schematic created using CircuitLab