I recently bought an Arduino Nano and when I try to find it in the Arduino IDE I cannot find it. please help. This is the error I receive when i try to upload a sketch, avrdude: ser_open(): can't open device "\.\COM3": The system cannot find the file specified.
What does Windows device manager say when you connect the board?
The board might require a driver if it's a clone (check for yellow exclamation marks).
If you have used an Uno before, COM3 is probably the port that is remembered by the IDE; does the IDE give you the option for an other port? See first paragraph above as well.