Carbon nanoparticles (CNPs) have drawn great attention in the last few years owing to their unique properties such as excellent water solubility, chemical stability, inertness, low toxicity, good bio-compatibility, and tunable photo physical properties. Recently, researchers have focused on hetero atom (N, S and B) doped CNPs due to their excellent properties. These properties make the CNPs and doped CNPs as potential candidates for a wide range of applications. For example, metal ion detection in aqueous solution, bio-imaging, bio-sensing, photovoltaic devices, cleavage of deoxyribonucleic acid (DNA), and catalysis. Therefore, CNPs are alternative to inorganic semiconductor nanoparticles. However, CNPs with diameter less than 10 nm have been prepared using various approaches including top down and bottom methods. Cutting the bulk carbon from high dimensional to zero dimensional by using either physical or chemical process are classified as top down method. Bottom up method refers the conversion of organic precursor to nano-carbon by using thermal pyrolysis, microwave based hydrothermal method, cage opening of C60 molecules. In the present work, I have dealt with the facile synthesis of CNPs and different hetero atom doped carbon nanoparticles (N-CNPs, B-CNPs, and BN-CNPs) using the hydrothermal method. Based on their intriguing physical and chemical properties, these CNPs/doped-CNPs have been explored for various applications such as (i) metal-free catalysts, (ii) color tunability from red to blue and bio-imaging, (iii) ammonia sensing, (iv) white light generation, and (v) detection of picric acid (PA) in aqueous solution. Finally, I have presented 3D nanodendrites of N-CNPs and Pd NPs and their excellent catalytic mass activity for methanol electro-oxidation and ultra-fast reduction of 4-nitrophenol.