For the YIP award, I proposed to assemble single ultracold molecules, where all quantum degrees of freedom are controlled, from individually trapped atoms in the gas phase. These individual molecules are like "Lego pieces" that can be assembled to construct more complex systems. The meticulous work to control all quantum degrees of freedom and the preparation of these molecules at the lowest possible energy allows these "Lego pieces" to follow rules of quantum mechanics, which are the underlying laws of atoms and molecules. By constructing complex systems from simple building blocks where their interactions are controlled and manipulated in the quantum regime, we aim to ultimately quantum simulate and compute complex systems for applications in chemistry. Another goal utilizing these novel sources of single molecules is to study chemical reactions in the full quantum regime and to prepare the exact number of reagents participated, which will allow us to unambiguously identify the nature of the reactions. During the award period, we demonstrated making one molecules from two atoms. We built an apparatus and devised many new techniques to allow two different species (cesium and sodium) of single atoms to be trapped,cooled, and transported in optical tweezers. We studied collision in a new regime where the number of collisional partners are prepared exactly. To coherently convert a pair of atoms into a diatomic molecule, we gained control of the quantum motion of individual Cs and Na by Raman sideband ground-state cooling. We achieve cooling outside of the so called Lamb-Dicke regime, which is a new regime from what has been demonstrated previously. After gaining motional control of individual atoms, a Cs and a Na atoms are merged into the same tweezers while maintaining them in their ground states.