The easiest way to tune a bass is using an electronic tuner. As a beginner, this will be the best way for you to tune. This method also does not require you to "hear" the notes, making it ideal for quick tune-ups between songs on stage.
Electronic tuners come in a wide variety, but none are difficult to decipher. Usually, you'll have a standard 1/4 inch jack for your instrument cable to plug into and a display telling you if your notes are sharp or flat.
To use an electronic tuner, plug in, turn the tuner on, and play a note. If nothing happens, you probably need to turn up the volume knob on your bass. If nothing still happens, you probably need to switch the tuner from "guitar" mode to "bass" mode.
The tuner will show your pitch. Keep playing the note at slow, regular intervals and adjust the tuning of the string. Watch the tuner's display to get the pitch right on target. Repeat for each string. You may find that the pitch the tuner picks up from the bass wavers around a bit each time you pluck a note. If so, let the string ring for a few seconds and watch where the pitch settles.