Blazars are known to be the most energetic sources (apart from gamma-ray bursts) we can observe in the Universe. They constitute the brightest type of radio-loud active galactic nuclei whose Doppler boosted relativistic jets are close to our line of sight. Blazars release a tremendous amount of non-thermal radiation throughout the whole electromagnetic spectrum, and often exhibit outbursts. These outbursts generally last between a few days and several months. The fast and frequent variability characteristics of many of these sources make possible detailed multiwavelength time-domain analysis. Also, we study the evolution of their spectral features in order to constrain physical mechanisms that drive the radiation production within the jets. After introducing the most common methods used to discriminate between leptonic and hadronic scenarios, we report studies on the flat spectrum radio quasar 3C 454.3 (one of the brightest blazars in gamma rays) to show how time-domain and spectral analysis can provide constraints on the size and the location of the gamma-ray emitting region. We also present our work with optical data obtained from South Africa based telescopes to carry out multiwavelength studies of blazars.