To record good narration for your video, you will need a microphone. A handheld microphone can give you the quality you need; microphones that are built into cameras and computeres are generally undesirable because they cannot help but pick up machine noise and are designed to record all sound in a room, not just one speaker.
You want to make sure this audio is free from noise as possible. Recording in a quiet, "dead" (not prone to echoing) room is best - even your car can work, if you’re recording into a portable system. And be sure to remember:
Be sure that you have printed the narration you need to read in large, easy-to-read type. Avoid breaking sentences and paragraphs onto separate pages, as this will break the flow of reading, and microphones will pick up rustling papers.
Hold the microphone far enough away from your mouth so that it doesn’t pick up hisses or pops as you exhale air into the microphone -- 'B', 'K', 'P', 'H', 'CH' and 'S' sounds are usually the worst offenders. Sometimes, pointing a microphone at your mouth from the side can help. It’s also helpful to listen to what you’re recording with headphones, if that’s possible with the system you’re recording on.
And finally, read slowly and clearly. Narration is not meant to sound like conversation; if you feel you are reading too slowly, you're probably at just the right speed.