Abstract: Given a smooth projective variety X over F_q, a natural question is what is the size of X(F_q^n) for all n. This question leads to the famous Weil conjectures. In this talk, we will talk about the first tiny element of it called the Grothendieck-Lefschez trace formula, which finds X(F_q^n) in terms of alternating sums of traces of Frobenius maps acting on l-adic étale cohomology of X.