The three-jets and $Z$ + jets cross-section measurements in proton-proton collisions data collected with the ATLAS experiment at the LHC

The thesis reports the cross-section measurements of the three-jets production and the production of jets associated with a $Z$-boson, $Z$ + jets. The measurements are performed using proton-proton collision data with centre-of-mass energies of 7 and 8 TeV. The data were recorded by the ATLAS detector at the Large Hadron Collider. The cross-sections are measured double-differentially as a function of jet kinematic variables. The results probe the strong interaction dynamics at high energy scales and provide a testing ground for the theoretical models used to describe the fundamental content of matter and interactions. The measurement accuracy is consistent with or exceeds in some regions of the phase space the accuracy in the next-to-leading order calculations in perturbative Quantum Chromodynamics. Thus, the measured cross-section is one of the necessary inputs for refining the description of the parton content of the proton and constraining its uncertainties. In addition, two measurements are reported that improve the accuracy in the jet energy measurement in the ATLAS experiment. One is the measurement of physical noise associated with the excessive energy deposits in the hadronic calorimeter due to simultaneous proton-proton interactions. Another is a jet energy measurement via the transverse momenta balance in events with a jet and a $Z$-boson. The results of both studies are used in the ATLAS experiment to accurately reconstruct and calibrate jets. Overall, these results provide an improved means for exploring new energy frontiers of particle interactions.