Finger tapping on guitar is a great way to get some cool sounds from your guitar it is a modern technique and is used a lot today. This technique is utilized by numerous players one main one is Eddie Van Halen. He uses this concept very well. Finger tapping is performed without using a pick. Instead, it is done by tapping the strings on your guitar using both hands in the process.
One handing finger tapping
Get hold of your picking hand then reach over to the fret board, have your eyes set on one particular string then simply tap the string then simply brush it downwards making a sound.
Two handed finger tapping
Two finger tapping is more difficult than one finger tapping because you have to use two fingers in coordination with each other and you have to get the timing right. However, with practice you shall get better and coordination won't be such a problem. First of all, with your fretting hand, just simply pick a single note on any string, keep your finger on it but don't play it. Now using your would be picking hand, simply pick a different note on the same string as your fretting hand. Tap the string hard and then brush it downwards using the flesh of your finger then release, hence making a sound. After this the note played by your fretting hand is immediately sounded. When you pick a note with one hand make sure that it is within the same scale as the other note that is played. This happens very quickly. Repeat this action and as soon as you have done it accurately then increase the speed.
As soon as you have mastered this then try moving your fretting hand to play another note including playing the first part and take in turn with each hand changing the note. This will give you a longer riff to play and make it sound a bit more interesting.
Keep practicing this until you get the coordination right as it takes time for your muscles to get used to it. You will eventually develop muscle memory and will then appear easier for you and not much thought is required. As soon as it appears easy try increasing the amount of notes adding one more note each time. Eventually try playing up the guitar using all 6 strings. Feel free to add some distortion to the sound and why not use some reverb it will make you sound like a cool guitarist. Keep practicing every day trying different notes. You will find yourself creating your own licks and riffs in no time.