Your own physical characteristics and abilities need not match those of your chosen character but it can help you in your adventuring career if your actual physical skills are congruent with your character's fantasy skills. The NERO system does allow players to play characters that are very different from themselves and still be able to prosper.
You must pick one of these classes:
Fighter
Fighters take naturally to the physical combat arts and rely mainly on strength and stamina to accomplish their goals. Human Fighters can wear almost any type of armor some races may have restrictions on the amount and types of armor they can wear, regardless of class, however.
Rogue
Rogues have a natural bent towards dexterity-based skills, and also the practice of alchemy, tinkering and trap making. Rogues are limited in how much armor they can wear. The lower Body Points, lighter armor and relatively high costs for combat skills does not make them well-suited for frontline combat roles.
Scholar
Scholars are adept at many mental skills and readily learn the magical arts. Scholars are even more limited in how many Armor Points they can use than are Rogues.
Templar
Templars are spellcasters and archers who are somewhat more adept than Scholars at physical combat skills. They are not religious in any way; NERO specifically prohibits religion in the game. Their combat training leaves them better able to fight but takes away from their studies. They cannot use as many Armor Points as Fighters, but can use more than Rogues and Scholars.