The uncertainty in tau neutrino production in high energy proton interactions has been the largest uncertainty in current and future tau neutrino measurements, preventing a precise test of lepton universality in neutrino scattering. DsTau (NA65) at the CERN-SPS is a recently approved experiment, which aims to study the problematic tau neutrino production. The main source of tau neutrino production is through the decay of Ds mesons, namely $D_s \rightarrow \tau \nu_\tau$ and then $\tau \rightarrow \nu_\tau X$. There is no data on the differential production cross section of Ds in proton-nucleus interactions, which leads to a large uncertainty of tau neutrino cross section measurements. DsTau addresses this issue and will provide essential inputs for future tau neutrino experiments. A large amount of charmed particles decay events ($\sim 10^5$) is expected to be detected as well, providing a possibility for interesting by-product studies, in particular a search for intrinsic charm in a proton. The experimental method is based on a use of high resolution emulsion detectors for effective registration of events with short lived particle decays. Here I present the motivation of the study, details of the experimental technique and the first results of the analysis of the data collected during test runs.