>>96690918 (OP)
What
>>96691187 said.
It's a roll-under system. You need 1d20 for basic checks and a set consisting of d4, d6, 2d10 and d12 for damage rolls, with vast majority of damage rolls being modified 1d10 roll (ranging from -3 to +5, but the bottom is always 1). In fact, if you squint, all you need is 1d20 and 2d10 to play Arcanum.
Unless you have expert training (or mastery for magic), actual success roll is capped at 95%. You can not have basic success lower than 5%
Sheet is already provided with the game, along with how sub-stats scale, so you can work that out easily.
Each 10 on tech aptitude is -1 modifier to spell rolls difficulty, each 5 on magick aptitude is +1 damage MODIFIER (which is a spell-specific multiplier to damage, not a direct bonus damage - aptitude 5 Harm does 6 damage, aptitude 100 Harm does 40)