The information about the NOC system is here:
http://www5.hrsdc.gc.ca/NOC/English/NOC/2006/Tutorial.aspx#6Basically if the 4 digit code starts with 0, it's a management position, skill type 0
Example:
0611 Sales, Marketing and Advertising Managers
If it doesn't start with 0 but the 2nd digit is 1, 2 or 3, it's a skill level A or B type position.
Examples:
5
111 Librarians
3
212 Medical Laboratory Technicians
7
316 Machine Fitters
If it's anything else, it's not skilled (low skilled or semi-skilled).
To qualify to apply as a skilled worker, you will need at least 1 year continuous skilled work experience (0, A or B).
For maximum points, you need 4 years skilled experience and to get that, you can add up different jobs and different NOC's as long as they are all skilled and you had those experiences in the last 10 years. Canada immigration counts a full time work year to be 1950 hours so if you have had part time jobs, you can calculate the hours and convert them into years of full time experience.