Trilium supports Markdown for both import and export, while trying to keep compatibility as high as possible.
If you want to import just a chunk of markdown from clipboard, you can do it from editor block menu:
You can also import Markdown files from files:
[[gifs/markdown-file-import.gif]]
You can export whole subtree to ZIP archive which will have directory structured modelled after subtree structure:
If you want to export just single note without its subtree, you can do it from Note actions menu:
If you want to export protected notes, enter a protected session first! This will export the notes in an unencrypted form, so if you reimport into Trilium, make sure to re-protect these notes.
See the dedicated page: Supported syntax