On the top of a note, use the syntax:
---
tags:
aliases:
whatever else you want to write:
---
to indicate frontmatter. Note that the main purpose of frontmatter is to give plugins a place to store user-readable metadata.
See the recent release notes on how to use tags and aliases. Note that these features are only available in Insider builds at this moment.
https://forum.obsidian.md/t/obsidian-release-v0-9-16-insider-build/8795