Meaning
A huge toothy grin, often showing both rows of teeth, under eyes narrowed into smiling arcs. The mood is proud, giddy or cheekily pleased with yourself, a beaming face more than a laughing one.
It works for small wins and playful bragging: “Passed my driving test on the first try 😁” It can also soften a mildly awkward moment, like admitting you ate the last slice. Because the teeth are so prominent, a few people read it as a nervous grimace, so add words if the tone really matters.