A chronological resume lists your work experience in order of time, usually starting with the newest job and working your way backward. Skills resume lists the skills you have acquired from each job and groups them together. For instance, "leadership" may be a skill, so you would have a section entitled "Leadership" and then you would list all the leadership skills and tasks you have done.
These are similar because you will still list all your previous work history, skills, accomplishments, etc but the difference is in how you categorize and list them.