Hammer-ons and Pull-offs on Bass Guitar

Hammer-ons and pull-offs are also known as slurs These two things refer to techniques employed by the left hand to sound notes without the direct aid of the right hand. You don't always have to pluck a note to play it. Hammer-ons and pull-offs let you play your notes using only your left hand. They are useful for playing quick bass licks with quick runs of notes and slurred notes, because they help to create a smoother sound between notes.

A hammer-on is a note you play by "hammering" a finger of your left hand down onto the string while it is still vibrating from a previous, lower note. when a note is sounded, and while it is still ringing, a left hand finger is used to quickly press down a fret that is on the same string, and close to the original fret. This will result in the sounding of the second note, even though the right hand did nothing but sound the first note. The vibrations that occurred from the sounding of the first note will be carried on to sound the second note.

Here's an example.place our index finger on the 3rd string, 5th fret, and sound that note. While the note is still sounding, we can use our ring finger to come firmly and directly down on the 7th fret of the 3rd string.

A pull-off is basically the opposite of a hammer-on. There are 2 notes involved. We can use a finger to fret a note, and then sound that note. While the note is still sounding, a finger can be placed directly behind the first finger, and then the first finger can be 'pulled off'. or
Before starting, you will need to have both left hand fingers that are involved already placed in their perspective frets. The first note is plucked, then a second note is sounded by pulling that finger off of the string with force. You are basically plucking the string with the left hand finger you used for the 1st note first note. You will need to pull both towards the floor, and out away from the neck of the bass.

For example, we could place our index finger on the 5th fret, 3rd string AND place our ring finger on the 7th fret, 3rd string. We can play the note on the 7th fret, and then 'pull' that finger off the string, which at the same time, will sound the note on the 5th fret. This is a pull off.
Here is a simple video for you.