With the idea of set, it can be understood that P is a set and Q is a set, but the whole range of P is in Q, that is, the range of Q is greater than P (P is indeed included in Q).
If you look for any element in P, you can find the corresponding element in Q, that is, the condition P can infer Q, and P is a sufficient condition for Q.
Looking for any element in Q may not necessarily find the corresponding element in P, that is, condition Q may not infer P, Q is not a sufficient condition for P, and P is not a necessary condition for Q (condition A can infer condition B, then A is a sufficient condition for B, and condition B can infer A, then A is a necessary condition for B).
To sum up, p is a necessary and sufficient condition for q.
(For those studying in Grade One, you can refer to it. )