Here are the rules for using attributes and skills in the School Hard setting.
Attributes
There are four attributes in School Hard: Brain, Brawn, Style and Substance. Between them, these attributes govern all actions, and whenever a character attempts to do something they will use one of their attributes to determine how successful they are. Of course, if it's something especially easy or boring then you can assume the character successfully achieves their goal. If it's something dramatic oor difficult, you will need to roll a dice and calculate a score to see if you're successful. More on that later.
Some actions, like a surprise exam will only have one relevant attribute - in this case Brains. Others may use any number of attributes depending on how the character goes about. A seduction attempt could use brains if the character tries to use logic to persuade their would-be paramour or impress them with their genius, brawn if they try to impress somebody by flexing their muscles, style if they bat their eyelashes, or substance if they, y'know, try to strike a conversation based on mutual interests and a shared respect. Of course, trying to seduce a chess club nerd by flexing muscles will be much more difficult than trying to impress them with you mad chess skills. It's important to be smart when you choose how to do something.
Broadly, Brains can be used for any action where being smart or intellectual may help. Brawn for anything where your physical prowess is key. Style for when you need to look good doing something, and Substance for when you can't fake it, and you need genuine talent or character.
As a guideline, a rating of 1 in an attribute is kittenishly weak, 3 is poor, 5 is average, 7 is good, 9 is amazing.
Skills
There are an indefinite number of skills. They reflect a specific way of using the attribute that a character is particularly adept at. So for instance, a band may have a talented guitarist who has a skill in substance (guitar). The same band may also have a guitarist with no talent beyond looking really good whilst playing the guitar - in other words, one who has a skills in style (guitar). Potentially any skill can be used by a character but they must be specific and make sense for the character.
Because skills are unique to people, a rating of even 1 means that character can do something better than most people, 3 is an impressive talent, 5 is semi-pro, 7 is professional, 9 is world-class
Doing Stuff
To determine whether a character is successful in her attempt to do something, simply roll a single D10 and add the result on the die relevant attribute score, as well as any relevant skill. The sum of these numbers has to equal or beat the target number, which will be set by the GM. Something that is of average difficulty will have a target number of 11, moderatly hard will be 13, difficult will be 15 and... well, you get the idea.