I so d@*m confused at this point between, toe, camber, etc, etc.
Toe: The inward or outward angle of the tire when looking down from above the car. If you look down at your feet when standing and move your toes together or apart without moving you heels, you know what toe is. This angle wears tires the most. It's there to take up slop in the suspension. Modern cars have very little slop so toe angles are smaller these days.
Camber: The inward or outward angle of the tire when looking from the end of the car. A bowlegged person has camber from the knee down (it's positive camber though). This is not considered a wearing angle, but it will amplify any alignment problems (particularly toe). Camber helps in cornering.
Caster: This is the forward or backward slant of a line drawn through the centre of the the ball joints when looking at the side of the car. This angle can cause vibration and cupping if it's too far out of spec. It's there to provide stability at high speeds. An example of too much caster is a shopping cart where one or more wheels oscillate back and forth.
SAI/KPI (steering axis inclination/king pin inclination): This is the inward or outward slant of a line drawn the centre of the ball joints when looking from the front/back of the car. This is considered a non-wearing angle. It's there to provide stability at low speeds (when caster doesn't have much effect).
TOOT (toe out on turns): This is the difference of the angle between the inside tire and outside front tire during a turn. The front tires don't turn on the same radius, so TOOT is used to minimize scrubbing. When perfect, the centreline of both front tires and the rear axle should rotate around a common centre of rotation--this happens at only one point during a turn. If wrong it wears tires very quickly in situations where there are many turn.
Ideally, the SAI and camber lines should intersect at the tire/pavement interface and at the centre of the tread. When they do this is called centre point steering (The DS-21 is an example of a car with centre point steering). Most cars don't have this, instead the intersect is below grade and the cars use power steering to overcome gravity (turning the steering wheel actually lifts the body of the car). If the intersect is above grade, then the car has no inherent stability.
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But I'm a complete newbie to performance tires, and other than looking at them to see if they look like they still have tread left, how do you measure whether you are getting to that point?
You measure with a tread depth gauge, but for the problem being discussed, looking to see if the tread depth is even across the tire is good enough. tread depth gauges range from simple to complex, but you only need a cheapie for this. Amazon has them for $3.00 and up.
What/where are the wear bars?
Wear bars are places in the tread where the tread depth is shallower. When the tire wears down, these places form a visible "bar" across the surface of the tread indicating that the tire is no longer legal for road use. They are indicated by marks on the tire's shoulder wherever a wear bar is. Different tire companies have different markings--some use a triangle Michelin uses a Michelin Man ( aka Bibendum).
