filmic - stopping unwanted bass notes is definitely a technique that you want to work on after you feel comfortable with your right hand position. If you are constantly refining your RH and still unsure of its functionality, I'd say don't worry about it.
As for the technique, simply put - you are (in some way) stopping bass notes from ringing. Either because of a rest in the music or because the bass note interferes with the clarity of the bass line and/or harmony. There are a few common ways of doing this.
Probably the simplest is placing your thumb back on the string of the bass note you played. Buy doing this, you'll stop the string from vibrating, thus "muting it" and "stopping" the note from ringing.
Another method is to use the left side of the thumb to gently touch the string vibrating to mute out the note. This technique is great when you are actually using the thumb to play another bass note on an adjacent string. This allows for the two bass notes not to ring into each other and clearly present the bass line and/or harmony change.
A 3rd way is to use a Left Hand fingering. This is probably considered more of an electric guitar technique. With this you reach an unused left hand finger up to stop the string. Sometimes if the right hand is very complex and doesn't have the ability to mute the bass note comfortably, this may be your only option.
Nick Cutroneo - Classical Guitarist, performer/teacher/suzuki instructor