As the previous educators have pointed out, reliability is all about getting consistent results from a study. In contrast, validity is the extent to which your study actually does what it sets out to do.
In terms of a relationship, what is interesting to note about reliability and validity is that they are not mutually exclusive. In other words, you can have a study which is reliable but not valid and, equally, you can have a study that is valid but lacks reliability.
There are ways to boost both validity and reliability. For example, if I am designing an assessment for my history students, I would want an assessment that tests exactly what I have taught in previous lessons. Every student should be given the same amount of revision time and the same set of instructions on how to complete the test, including how long they have to complete the test. When it comes to marking the tests, I will need to use the same mark scheme for every student. This will give me high reliability and high validity.
However, this relationship is further complicated by the fact that there are different types of validity and reliability, and all of these various measures need to be carefully considered when designing an experiment or study. Please see the reference link for more information on these.
For any researcher, then, the goal is to have a study that is both high in validity and high in reliability because this will provide a set of high-quality results from which to draw conclusions and make an analysis.