Giant radio sources are the largest single objects in the Universe. The projected linear size of their radio structures, larger than 0.7 Mpc, makes them valuable objects to study many astrophysical problems. It is still unclear why only a small fraction of radio sources reaches such a large size. It is considered that it may be due to special external conditions, such as lower intergalactic medium density. Other investigators pointed out the internal properties of the "central engine" or an advanced age of the radio structure and/or recurrent radio activity as a possible cause. In my Thesis I investigate the hypothesis that the giant radio sources can have very large radio structures due to specific properties of their central active nuclei. Because of lack of a representative sample of such objects, as many radio sources were not recognised to be giants, this hypothesis was not investigated in detail. By comparing the radio and optical surveys, a lot of gigantic-size radio sources have been recently discovered. I selected a sample of giant radio sources and compared the fundamental physical parameters of their active nuclei (such as black hole masses and accretion rates) with parameters of observed radio structures. As a result, I found out that when taking into account the optical and radio properties, giant radio sources have properties similar to those of smaller size and that giants do not have more powerful central engines than other radio sources. The results obtained in this work are consistent with evolutionary models of extragalactic radio sources, that predict that giants could be the more evolved (aged) sources compared with smaller ones. In addition, I discovered that the environment may play only a minor role in the formation of large-scale radio structures. In my thesis I showed out that giants have relatively large number of old star with solar-like metalicity. The stellar population composition of giant radio galaxies could be the only property that distinguishes them from other radio sources. This fact may suggest that different histories of the host galaxy formation may be the main reason why some of radio sources evolved to giant size.