What do sines stand for in warhammer 40000?

WS is the Weapon Skill of a particular miniature, ranging from 0 - 10, and it represents that miniatures ability to fight in close combat, a high skill means that that model fights better in combat....

Ballistic Skill.

WS - Weapon skill BS - Ballistic skill S - Strength T - Toughness W - Wounds I - Initiative A - Attacks Ld - Leadership Sv - Armor save

If you mean what do you fight for, it depends on what army you are playing. Space Marines, Imperial Guard, and The Inquisition are fighting in the name of the God Emperor, fighting to protect...

No, each types rules are very different.