Walking up or down into a chord is a really nice way of making a transition from one chord to another. The technique is also called a walking bass line.
It is used in country, bluegrass and jazz very often, but you can use it in other genres as well. At the most basic level, you can use it to add a bit of extra something to your chord progression and to liven your strumming patterns.
When we walk into a chord, we'll always be playing a baseline, so we'll be plucking the lower strings of the guitar. This can, of course, mean the low E string, the A string, or even the D string at times, depending on which chords we're working with.
Let's have a simple example to demonstrate walking between chords on the guitar. Here are the tabs and the audio clip of a simple chord progression with a walking bassline. Note that this is a I-vi-IV-V chord progression in the key of G in 4/4 time:
As I mentioned, we basically plucked a few notes of the key we're in, to lead into the next chord. But which notes do we need to pluck and why? Let's have a look at the details: