difference between tolerance and accuracy

There are two basic kinds of tolerance: engineering and statistical. Based on your question, I would guess you're asking about engineering tolerance. Engineering tolerance gives a range in which the part or feature is completely acceptable. That is, if you specify a shaft to be 0.500" +/- 0.005", you're saying that any diameter from 0.495" to 0.505" will work as well as 0.500" would.

Accuracy normally refers to a mesurement and tells something about the probable distribution of errors (uncertainities not mistakes). For example, you might mike a shaft and say that it is 0.375" +/- 0.008" and you mean that you are confident that, if you did a thousand measurements with some Gaussian distribution, you would find 68% of those (1 standard deviation each way) to be between 0.367" and 0.383". The uncertainty (which is a better word than accuracy) will be due to things such as measuring instrument resolution, temperature extremes, reading parallax, etc.

NIST has some good material on these things

http://itl.nist.gov/div898/handbook/mpc/mpc.htm