Trilium Notes supports importing Markdown restricted to the CommonMark specification (where tables are not supported )
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.