Reliability and Validity? A Level Psychology!!

For reliability, I think it's pretty much just how consistent replications are e.g. if an experiment has been tested by different people and it produces consistent results, then the experiment/study would be seen as reliable.

As for validity, there are various kinds:
Internal validity - this basically measures whether the study is actually measuring what it is supposed to be measuring e.g. if a study claims to measuring quality of attachment but does not acknowledge that different people have different attachments with different people, then it may be internally invalid

External validity includes ecological validity and population validity:
Ecological validity - the extent to which results can be generalized to real life settings.. so lab experiments are low in ecological validity while natural/field experiments are high in it

Population validity - the extent to which results can be generalized to a wider population, so if there is a small sample size, or the sample is all males, or all people from the same country, then it will be low in population validity

This is all just from the top of my head so hope i helped