Attributes

There are three main attributes.

Martial: The character’s ability to understand warfare and marshal his or her fighting forces in battle.
Charisma: The character’s ability to influence others.
Finesse: The character’s ability to get things done, despite obstacles.

Attributes range from 0 to 10 but modifiers caused by Traits can cause Attributes to be higher than their normal range.

Simplified you may say that a 5 in any attributes is mediocre and such character will do no harm or good.

Some character roles also gives bonuses for each attribute point above 0 and some actions gives bonuses based on the difference between characters.

So to sum it up: 0 = abysmal; 5 = mediocre; 10 = Best of mankind; 10 < Son of "insert your god's name here".

Martial

This is a Character’s ability to understand warfare and marshal his or her fighting forces in battle.

Useful for anyone who have a military connection.

With the latest patch, a Commander receives a +0.5 bonus to combat rolls in battle for every point of martial which he exceeds the enemy commander. Since base dice rolls vary between 1 to 6, a difference of a few martial points is very significant. Generally, never use a commander with less than 7 martial in battle.
Rulers, Ministers and Magistrates may give morale bonus.
Governors defend better when sieged.

This attribute is a Character’s ability to influence others.

Useful for everyone as it affects Popularity directly.

This attribute is a Character’s ability to get things done, despite obstacles. Probably the most important attribute for non-martial characters.

Useful for anyone in high positions.

Rulers, Ministers and Governors tributes more from their office.
Magistrates are better researchers. +10% bonus per point of finesse. A finesse 10 character doubles your research rate.