Validity is when you test what is supposed to be tested. For example, when you test Reading, you should not get your students to write a lot because you are actually testing Reading and in this way you are testing them Writing too and you should not also score their writing. So you should concentrate on Reading only.
Reliability is the consistency of the result of the test. If you give a test for specific students today and get a specific score and you give the same test to the same group of students another time and they get the same or not necessarily the same BUT near to the previous score then it is reliable.
Not a teacher but I know this piece of information and wanted to help. If I was wrong, please correct me.