It doesn't matter how great your bass line is; it will sound bad if your instrument isn't in tune. Indeed, an out-of-tune bass is one of the most common problems to frustrate beginning bass players. Changes in temperature and humidity can knock your strings out of tune, and even simply playing the instrument will slowly de-tune it as well.
You should tune your bass each time you pick it up, and you may need to re-tune it now and then while you play as well. Tuning a bass usually doesn't take more than five minutes, and as you get more experienced you'll learn to do it in less than 30 seconds. As a beginner, you may find tuning difficult, but the more you play, the better your ear will get and the easier it will be to hear those low notes.
There are a few methods commonly used to tune a bass guitar. Let's take a look at each one.