Upload a world from Windows

1. Press Windows key + R and open this folder: %localappdata%\Packages\Microsoft.MinecraftUWP_8wekyb3d8bbwe\LocalState\games\com.mojang\minecraftWorlds
2. World folders have random names. Open levelname.txt in each to find the right one.
3. Compress that world folder into a .zip.
4. In the panel , open Files, go to the worlds folder, and upload the zip. For big files use SFTP.
5. Unarchive the zip and note the exact folder name.
6. Edit server.properties and set level-name to that folder name. Save.
7. Start the server.

Add a behavior or resource pack

1. Download the pack. If it is a .mcpack, rename it to .zip and extract it. You need the folder that contains manifest.json.
2. Stop the server. In Files, upload that whole folder into behavior_packs (behavior) or resource_packs (textures).
3. Open the pack’s manifest.json and copy the uuid and version from its header section.
4. Open worlds, then your world’s folder. Create or edit world_behavior_packs.json (or world_resource_packs.json) and add:

[
  {
    "pack_id": "PASTE_THE_UUID_HERE",
    "version": [1, 0, 0]
  }
]

5. For more packs, add more objects separated by commas inside the square brackets.
6. Save and start the server.

If the server will not start, a missing comma or bracket in that JSON is the usual cause. Make sure the pack supports your current Bedrock version too.