The premises of the argument are among the things being taken for granted. The conclusion of the argument should be the point that is at issue. Each element of an argument that is presented as logically following from some other claims should actually follow from those claims. When we say that a claim follows validly from another, we mean that if the initial claims are true then the claim that follows must be true too. That is, it is logically impossible for the initial claims to be true without the latter one being true too.
Every turkey is a bird.
So some birds are mammals. If the premises were true, the conclusion would have to be true too. But one of the premises is false, and so there is no guarantee that the conclusion is true. Validity has to do with the logical connections between the parts of an argument. For example, if Judy keeps her pet penguin in the garage, the premises are true but the conclusion need not be true.