Why doesn't the car start on every attempt?

What is your question?

Nearly every time that I go out to start the vehicle I turn the key and it makes this ticking noise and it refuses to start. I will wait a few minutes (5-20 mins) and try again. Sometimes it will start right up other times it takes a few time of me doing this for it to start up again. Ive only had this car 2 months, I bought it used with 178,000 miles. A friend told me it was the battery.