The descriptions of these various knowledges and skills can be found in several books - Wilderness Survival Guide, Dungeoneers Survival Guide and Oriental Adventures. Some are not in any of these books, and if used, will require some 'common sense' thought. A few have been greatly expanded, with writeups that can be found on this site under the Crafting and Gathering Skills for Players link.
If being bought with Character Improvement Points, the cost is equal to the number of NWP currently possessed, never to exceed 5 (unless the base cost is 2 instead of 1, then double the cost).
Most NWP can be increased from one point to up to five points; this costs the same as a new NWP. In most cases, this simply gives the character two dice to check for success (performing a difficult action while mounted, building a fire, playing a song, and the like). In certain specialized NWP, it can mean something very different; these are covered under the Crafting and Gathering Skills pages.
To get an idea of what it means to have more than one point in a NWP, here's a rough guide. In general, each point you have in a proficiency gives you -2 on the roll to check for success, though a 20 is always failure (Wilderness Survival Guide, page 12).
1 - you spent perhaps 80 hours learning this, so you are competent. Something like having taken a semester of a subject in college.
2 - your training is at the level of an undergraduate student, or someone who has practiced or studied for a couple of years.
3 - your training is at the level of a graduate student or professional with years of experience.
4 - your training is at the level of a professor or doctor.
5 - you have an almost superhuman level of knowledge or skill, at the peak of mortal ability. Steven Hawking, Roger Federer, Babe Ruth, Napoleon.
# slot indicates how many NWP points they cost to buy.
Modifier is the adjustment to a d20 roll, which is compared to the listed Attribute; you must roll equal to or below that attribute to succeed. The further below the attribute you roll, the more successful you are.
In some cases, no roll is needed unless something unusual is being attempted, such as riding.