Recent JWST observations have revealed a wealth of detail about high-redshift galaxies, including strong [OIII] emission and clumpy structures. To interpret these observations, we utilize FirstLight zoom-in simulations with pc-scale resolution. This talk will discuss: (1) the physical properties of [OIII] emitters and the use of line diagnostics, (2) the formation of clumpy galaxies through major mergers, and (3) explanations for the unexpected abundance of UV-bright galaxies at $z>10$, including the role of high star formation efficiency and dusty outflows.