library not working

arduino simple frequency library is not showing in the software and i am unable to upload it on the arduino uno!! please help....

Arduino come with some libraries but not all ever made. You have to download it and import it in Arduino IDE (or extract it in the right place).

So, what have you tried?
Which library exactly? (LINK!)
Did you download it?
What errors?
What code?

Google can't find any library named "simple frequency library".

Did you mean the Simple Audio Frequency Meter tutorial for the Arduino Zero? https://www.arduino.cc/en/Tutorial/SimpleAudioFrequencyMeter That won't run on an Arduino Uno.