Advances in quantum manipulation of molecules bring unique opportunities, including the use of molecules to search for new physics, harnessing molecular resources for quantum engineering, and exploring chemical reactions in the ultra-low temperature regime. In this talk, I will focus on our work developing techniques to build single ultracold molecules in optical tweezers as a versatile platform for quantum simulation and quantum computation. Starting with the first proof-of-principle demonstration of building a sodium-cesium molecule from two atoms, we progress to obtain full internal and external quantum state control of a single rovibrational ground-state molecule recently. I will explain how these single molecules will be used as valuable resources for future quantum entanglement applications due to their rich internal degrees of freedom and strong dipolar interactions. If time allows, I will touch on a separate work in the area of ultracold chemistry, where we work toward a detailed microscopic picture of chemical transformation of molecules from one species to another.