The Cosmic Rays (CR) were discovered over a century ago through a pioneering balloon flight by Victor Hess in 1912. The energy range of these particles spans from a few MeV to $10^{20}$ eV, where the flux rapidly falls off with the increasing energy. Although Supernovae, Active Galactic Nuclei, Quasars, Gamma-ray Bursts, etc., could be the potential sources of CR particles, the origin of these particles is still unknown. One of the possible ways to identify the sources of CRs is by detecting the non-thermal gamma-ray and neutrino emissions from Giant Molecular Clouds (GMCs). GMCs are massive, dense areas of gas and dust in the Interstellar Medium (ISM) that are essential for creating stars and planets. The electrons and protons both can produce gamma rays through leptonic processes like Bremsstrahlung or Inverse Compton and hadronic processes like pp interactions. However, neutrinos can only be created by hadronic processes (CR interaction with the target ISM material). Therefore, detecting neutrinos is the key to revealing the CR sources. In the era of multimessenger CR astrophysics, GMCs have become more crucial to pinpoint possible sources and accelerators of CRs.

In this presentation, first I will give you an overview of CRs and their interactions with GMCs producing high-energy radiations (like gamma rays and neutrinos). I will talk about my work of explaining the observed gamma-ray flux from Rho Oph, Aquila Rift and Cepheus GMCs using a detailed Monte Carlo simulation where an excess in the flux was previously reported. The excess was postulated to be coming from several 100 T--Tauri stars in GMC environments that could inject an extra component of CRs that, interacting with the gas medium, can produce additional gamma rays. However, using our detailed simulation framework, we have explained the observed gamma-ray spectra for all the GMCs quite satisfactorily. I will also discuss the results of our ongoing works to explain the diffuse gamma-ray and neutrino emission from the Milky Way Galaxy, focusing on contributions from GMC alone.