Before you commence each lesson or practice session you must tune your bass. If your bass is out of tune everything you play will sound incorrect even though you are holding the correct notes.
If you want to play along with the recording your bass must be tuned to "concert pitch". This is a standard tuning that all musicians tune to so that they can play "in concert" with each other. It is possible for a bass to be in tune with itself (e.g., you play a scale and it sounds in tune) but out of tune with a piano which would be tuned to concert pitch.
Written on the following page is a method of tuning which all bass players must know, i.e., tuning the bass to itself. This tuning method is essential to know because when tuning to concert pitch you may only be given one note (usually the open third string A) so you have to know how to tune the other strings to this note.