Hello, I am new to the world of programming and just revived my arduino UNO. I am looking at the board and have questions about some of the markings next to the pin holes. Here are the ones I would like to know about:
The reset pin: what is it and what dose it do in general.
The 5V pin: dose it always send out 5V or only when instructed to?
the Vin pin: what is it and what dose it do in general.
Thanks in advance. 
--ArduinoN00b--
The reset pin: what is it and what dose it do in general.
As the name implies, it will reset the processor. Normally it is pulled to 5v with a resistor, connect it to GND (then release) to reset.
The 5V pin: dose it always send out 5V or only when instructed to?
Always, connected to the output of the 5v regulator.
the Vin pin: what is it and what dose it do in general.
Connected to the DC barrel socket, that's where the power comes in from your plug pack if you are using one.
Rob