Okay, so the basics (bare bones of what you need to know).
Accuracy refers to 'whether it matches scientific fact'. If you are using a value which is accepted by the scientific community/came out of a textbook/should be the value you get in your hypothesis. Does your data match that? Also, if the calculation of the total experimental error is greater than the error due to measurement, your experiment isn't accurate.
Reliability refers to the credibility of your data. Often an investigation is reliable if you have repeated it (with similar results), excluded outliers and taken averages.
An experiment can only be valid if it is BOTH reliable and accurate. If it is reliable but not accurate, or vise versa it cannot be considered valid. And if an experiment is not considered valid then the aim has not been achieved.
That's the bare-bones of it all.
Good Luck!