If you take a deep view of the matter, you end up with the idea that "chord" and "riff" - or "chord" and "melody" - are just the "vertical" and "horizontal" aspects of _harmony_.

To keeps things simple we can say "harmony" is combining tones in a pleasing or artful way. Those tones can be combined literally by playing multiple tones simultaneously, or played in succession. So, for example, using a simple `E` major chord, we can play the chord either vertically or horizontally... 

[![enter image description here][1]][1]

The first way, the vertical way, is the way most people think of harmony. They think of harmony literally as playing chords. But the second way, the horizontal way, is also working with chords and harmony, although you might want to think of it as _implied_ chords and harmony. But to make the point clear, if you played some thing like this... 

[![enter image description here][2]][2]

...it will be heard harmonically as chords `E A E`.

When you break up chords and play them in that kind of linear, horizontal fashion, it is technically called _arpeggiation._

A very important aspect of harmony and horizontal lines is "filling in" the spaces between the tones of the chord. If, for example, I stick notes in between the notes of the arpeggiated `E` chord, I get this... 

[![enter image description here][3]][3]

...I used white note heads for the "in between" notes to make it easier to see that the black note heads are the tones of the `E` major chord (`E G# B`.) The technical name for those in between notes is _non-chord tones_ (NCT.) There are many kinds of NCTs. In this example they are called _passing tones._

So, in that example we can see there is _both_ the first five tones of the `E` major scale, but _also_ and arpeggiation of the `E` major chord with two passing notes. The point bears repeating: those five notes that most would regard as part of _only a scale_ also function harmonically as a manifestation of a _chord_.

Now let's look at a real music example of those ideas in action... 

[![enter image description here][4]][4]

...in that riff all the notes except two are tones from an `E7` chord (`E G# B D♮`.) The `G♮` and `F♯` can both be regarded as _neighbor_ or _auxiliary_ tones, which mean to take one step away from a chord tone and then go back. Technically the `G♮` is an "incomplete" neighbor, but it works the same way, or call it a passing tone if you like. 

But notice that the `F♯`, which I call an auxiliary tone, is not literally a move _immediately_ from the `E` and _immediately_ stepping back to the `E`, there are other notes in between. This kind of thing happens where harmony is regarded in a horizontal way. We can think of those `E` and `F♯` notes as persisting in memory.

Just like we took a chord of simultaneous tones and broke it up by arpeggiation into a horizontal line, we can work in the reverse and take a horizontal line and _reduce_ it to the implied chord. To show how the `F♯` is acting like an auxiliary to `E` we can reduce the riff to this... 

[![enter image description here][5]][5]

Back to your question...

> ...replaces the need for chords, instead using riffs and licks etc, but still keeping up a nice chord progression. My confusion in trying to learn this is how you can follow a chord progression using only notes or riffs?

  - emphasize arpeggiating the chord tones
  - fill in between the chord tones with non-chord tones
  - use tones from the blues scale, or relative to the chord use flat thirds, flat fifths, and flat sevenths, for a bluesy feel
  - don't worry about using a small range, many riffs dwell around three adjacent tones for a while
  - in terms of pitch, your basic material is just chord and scale tones, which is generic, think of _rhythm_ as a primary way to give riffs a unique character
  - in terms of direction, your basic material is up and down, which is also generic, so use some jumps in the riff to give them a unique shape, for example instead of `E G♯ B G♯ E` you can try `E B G♯ E B`


  [1]: https://i.sstatic.net/K6K0t.png
  [2]: https://i.sstatic.net/WsFU0.png
  [3]: https://i.sstatic.net/ziclX.png
  [4]: https://i.sstatic.net/portt.png
  [5]: https://i.sstatic.net/yE3Uf.png