Ok, first of all, skill points. They determine what your tamagotchi grows into and what job your tamagotchi will get in adult stage. Skill points are earned by playing games.
Secondly, jobs. When your tamagotchi is an adult, it will receive a [!] letter, inviting it to get a job. Depending on your tamagotchi's skill points, it might not be able to get various jobs, due to low fashion skill, cleverness skill or kindness skill.
Could you perhaps provide more information on what you don't understand, then maybe I could give you more help?