Install Obsidian from https://obsidian.md
Open Obsidian
Create a new vault
Choose a vault name
Choose a vault location on your device
Click Create
Create notes inside the vault
Create folders for organization (optional)
Add content to notes
Link notes using wiki links like [[Note Name]]
Use backlinks by clicking linked note references
Sync the vault (optional) via Obsidian Sync or Git
Enable desired community plugins (optional) in Settings → Community plugins
Adjust settings (optional) in Settings (themes, editor, file handling, hotkeys)