Ever since we first laid eyes on the twinkling lights in the night sky, our species began its age-old quest to understand how we came into existence as a planet and what the future holds for it. Most of the traditional formation theories of planets were anchored on the examples drawn from our own solar system. With the surprising and emerging trends among the yet incomplete exoplanet demographics, we are at the wake of a rigorous revision of our theoretical understanding of how planets form and evolve. To form accurate theories however, it is necessary to base them on a planet population that spans the complete range of parameter space not only in terms of its physical properties like mass and orbital separation, but also with respect to the type of stars that host these planets and their age. In this regard, direct detection, whereby you measure photons coming from the planet, helps one get closer to the whole picture since the ideal target population for this technique are young, giant planets in wide orbits that are generally difficult to observe with other detection techniques. Over the last few years, the sensitivity reached by direct imaging observations has seen tremendous improvement owing to the use of high-contrast tools like coronagraphy and adaptive optics. The development of high-resolution spectrographs together with advanced post-processing techniques have recently, for the first time, enabled witnessing planets while in the process of being born, helping us understand how they grow by devouring material from the planetary nursery — a mechanism known as accretion. This is an exciting era for planetary science, with many ongoing as well as planned future surveys with both ground and space-based telescopes dedicated to unravelling the mysteries surrounding the origin of planets. 

In this thesis, I provide an overview of direct detection as a tool to study sub-stellar objects – a categorisation that includes both planets and brown dwarfs, and whose blurred lines of distinction is a point of contention in astronomy today. I concentrate my discussion on two techniques, high-contrast imaging and high-resolution spectroscopy, both of which have proven significant in the race for planet detection and characterisation. Three scientific research works are carried out as a part of this thesis, using which I highlight the benefits of these techniques in constraining the physical properties of planets and brown dwarfs, as well as obtaining clues to their formation mechanism. In Paper I, I search for a Jupiter-like planet around a nearby Sun-like star that has long eluded imaging surveys, revealing its presence only via its influence on the parent star. I show how the brightness constraints at various separations and multiple wavelengths from the parent star help set a lower limit on the vaguely defined age of the system, in the absence of detection of the planet in our observations. In Paper II, I report the discovery of two low-mass companions to a massive, bright, young star, infer their orbital dynamics from multi-epoch imaging data, and constrain their physical properties using simultaneous low-resolution spectroscopy. In Paper III, I use a high-resolution spectrograph to observe for the first time, resolved Hydrogen and Helium emission lines from a young, isolated planetary-mass object in the midst of formation. Based on analysis of these line profiles, I obtain clues to the possible accretion mechanism at play in this nebulous cosmic phenomenon.