resistors

I realize resistors can have the same values say 100 ohms and be different sizes. I also noticed they have different dispensations or something like half a watt what does this and the size of a resistor mean?

like half a watt what does this and the size of a resistor mean?

It is not a size it is a rating. It tells you how much power the resistor can burn off before the resistor burns up.

so the only difference with a larger resistor is it is safer?

And physically larger and more expensive.
It is rare you will dissipate more than 1/8 th of a Watt in normal electronics. You only need higher wattage resistors in power circuits.

Resistors restrict current flow by resisting it. A by-product of this resistance is heat. A resistor can only stand to dissipate so much heat before it is damaged.

A 100 ohm resistor connected between 5v and Gnd will dissipate 250mW. (1/4W) So, a 1/4W resistor can juuuust do this without catching a permanent tan. A 1/2W resistor can handle this all day and all night. In reality, as a designer, you would not push a component to the limits. You want a safety margin, so you'd use the 1/2W even though the 1/4W is technically rated to handle this.

Now, up the voltage to 7v, and the 1/2W is starting to sweat, while the 1/4W would be nothing but a sweet memory, and a 1W resistor would be snoozing peacefully.

At 10v, the 1W is OK, but cooking nearby eggs, the 1/2W is crispy as bacon, and the 1/4W is just a funny smell in the air.

Double the resistance, and because less current is flowing, less energy is wasted as heat, and things run cooler. Now your 1/4W, 200 ohm resistor between +5v and Gnd is barely warm.