What is lube?
Answers: Lube is short for "lubricant" or "lubrication." Lubes are usually referred to as artificial moisture and are purchased over the counter. KY is very popular, but near are some other very honest ones (go to http://www.adameve.com for a HUGE selection of lubes). I one-sidedly prefer either ID or Astro-Glide.
In a serious pinch, you can use saliva, but NEVER EVER use grease or Vaseline...especially if you're using condoms.
Lubes are applied (a little bit at a time!) to the vaginal entrance, labia, and/or the penis prior to penetration to take home it easier and more comfortable. While the vagina is self-lubricating, as you age or use different meds, your vaginal moisture can change, so artificial moisture is a must.
Lube can also cause manual masturbation easier and more nice, because the clitoris is very sensitive as is the penile shaft, and making things slippery is a VERY fitting thing for pleasure.