Nowadays, there are significant selection effects in searching for quasars. To get a complete census of quasars, we can't just look at those objects which have excess UV light compared to stellar sources, because quasars reddened by dust are not negligible and should be considered. In my master's project, we mainly focus on the red quasars. We got the spectra of 50 quasars using the NOT and the GTC, with which we show the necessity of a spectroscopic selection of quasars. Moreover, we are attracted by the detached quasars in the objects we have observed. They don't show obvious emission features in the optical band, which makes it extremely difficult to determine their redshift. However, we found a quantitative method to measure the onset of the Lyman-alpha forest, which can help in the determination of the quasar's redshift. Besides, a tentative dusty wind model illustrating the inner structure of the outflows from quasars is proposed, to interpret the peculiar spectral features in detached BAL quasars