Proficiencies are a list of unique skills and/or jobs which the player can have knowledge and skill in which have an actual impact on the game mechanics. This can involve crafting skills, affect combat in some way, chance of survival, and so forth. Proficiencies are percentile based, but mostly use a d20 since bonuses and penalties, as well as 'to hit' numbers are all by 5% increments (100 divided by 20 is 5). As a result, proficiency rolls require low rolls, not high rolls.
Proficiencies are divided into three categories: Unskilled proficiencies (broken further into 'any use' and 'trained use' skills), and Skilled proficiencies. "Any Use" skills do not require proficiency points in them to use. The base chance to succeed with this roll is a 1-2 on a d20 (or 10%). "Trained Use" skills can never be used unless the character has proficiency points spent in them, making them skilled proficiencies.
To know the full extent of skilled proficiencies, one must understand the points system. All players start out with four proficiency points at level one. For every three levels, they will gain an additional two proficiency points. These points can be spent on any proficiency they wish, thus players can be jack of all trades master of none type players, or they can spend most of their points on specific proficiencies to increase their chance of success. When a skill becomes a skilled proficiency, it's base chance is increased to 1-5 (25%), and is increased further by an additional 1 (5%) for each additional proficiency point added into the skill.
On top of this, the player should apply the attribute modifier. This modifier is the same as the Ability checks table. Example: in the following table, if Strength is 14, then any proficiency using a strength modifier will gain a bonus of 1 (or 5%) to the base chance.