To many people cool riffs are what guitar playing is all about. I guess most people would like to pick up a guitar and casually play a riff that was part of the soundtrack to the life of at least one person in the room. Of course, learning to play riffs on the guitar is not the same as learning the guitar. If you have learned to actually play the guitar you have the knowledge and the expertise to write your own riffs and songs. But maybe that is too much trouble.
This brings us to the first condition necessary for impressing your friends and acquaintances with your guitar riff playing: do not try this in the presence of someone who can actually play the guitar. If you are seeking to be remembered as person who has interests other than your clothes and hair, and if you want to be seen as having hidden depths in your soul, playing your riffs in the presence of a real guitar player might not have the desired effect.
You see, if you attract the attention of a genuine guitarist he is going to want to see what else you can do. He is going to want to swap licks and riffs with you. He will start a conversation about amps and Strats, stomp boxes and coaxial cables. This is not a good conversation for you to hold your end of up. In fact no holding of ends should be attempted, just mutter something about being out of practice because of a skiing accident and back off.
So we have established that any guitars you find lying around should be the property of people who once wished to learn to play but stopped. Okay, no problem, there are many such guitars lying around. So now we know the ground rules, where do we learn the riffs? Assuming that you cannot read music, your choices lie in the directions of learning by ear and learning to read guitar tabs.
Usually learning guitar riffs by ear needs some practice with the guitar but if you have the time to spend a non music reading faker like yourself can to learn guitar riffs by ear using an electronic guitar tuner. The tuner you want has a visual interface that tells you the names of notes being played into your computer’s microphone. You can download these guitar tuners from the internet. Just do a search for free guitar tuners.
This is a way for a real musician to learn a small section of music quickly but I do not seriously believe a non-guitar player will really have any success with this method. The realistic course is to download the tabs to your riff and learn to read tabs. It is not difficult and it will help if you download one of the free tab editors like Powertab. These play the music and a cursor follows the music on the tab. Another good tab editor is Tabledit. Guitarists who make their own tabs publish their work for free on the net as files that can be played and read in Tabledit or Powertab. If you seriously just want to learn to play cool riffs this is your best option.