Has anyone ever written a sonnet? What does ABBA mean in the format? What else is iambic? I don't understand it at all. I need it

This is a form of poetry with fixed lines handed down from ancient Europe. The format you proposed is roughly like this. The content at the beginning and the end are similar, singing and sighing. The content in the middle is similar, whether it is the meaning of the poem or the scenery. Iambic means that when writing a poem, if a step has two syllables, the former is lighter than the latter, then the step is called iambic, the light reading is "suppression" and the stress is "yang", so it is called iambic. It's a bit like the flat rhyme in China's classical poems. I am a light learner, so I will speak a little. I hope it helps you.