The CMS experiment at the CERN Large Hadron Collider (LHC) has a redundant muon system composed of three different detector technologies: Cathode Strip Chambers (CSC, in the endcap regions), Drift Tubes (DT, in the barrel region), and Resistive Plate Chambers (RPC, both in the barrel and endcap). The RPC are designed mainly as a trigger detector but they contribute to the muon reconstruction as well. Thus the monitoring and analysis of the system performance are necessary and essential for the final data quality. The main detector characteristics and the hit efficiency and cluster size are presented in this thesis. The stability of the system in the conditions of high instantaneous luminosity and high number of pile up (PU) events are presented in a view of history monitoring and stable trend. RPC background, currents and charge was studies in depth with increasing luminosity and data driven estimations of all these parameters are reported at the extreme conditions of High Luminosity LHC (HL-LHC). First measurement of the top quark pair production cross section ( t t) in proton proton collisions at a center-of-mass energy of 5.02TeV is presented as a second part of this document for 27.4 pb?1 data collected by the CMS experiment at LHC. The measurements are performed by studying events containing at least one charged lepton. The measured cross section ist t= 69:5 6:1 (stat) 5:6 (syst) 1:6 (lumi) pb, with a total relative uncertainty of 12%. The result is in agreement with the expectation from the standard model. The impact of the presented measurement on the determination of the gluon distribution function is investigated.