reading resistor with a digital multimeter

If I read a 100 ohm resistor, brown - black - brown - gold,  I get 100 on my meter  or 99

Yes here it works good right!, but what you have to note here is that the value is displayed in ohms. Look for the symbol on the multimeter. 

when I read the resistor orange - orange - brown - gold which is a 330 ohms I get .334 reading on my digital multimeter.

Now here also the meter is working fine, you are just failing to notice it. The reason is now your multimeter is displaying the value in Kilo ohms. Look for the symbol on your mutimeter it will have a "K". 

So 1 Kilo Ohm is 1000 Ohms. Hence 0.334 Kilo ohms is 334 Ohms which is close to the actual value of 330 Ohm. Hope you got it clear now.

If you are new with multimters then you can read through this below tutorial 

https://circuitdigest.com/article/how-to-use-a-digital-multimeter

It depends on how the meter was programmed to show values. In your case the meter has been programmed to stay in "Ohms" mode if the value of resistor is eqaul or less than 100 Ohms. If greater then this value then the meter would get into " K Ohms" Mode

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Thank You for any help

John