When the file/-s in the zip-folder …
- is/are an .mcaddon/.mcpack
Just double click😉. Minecraft Bedrock opens and loads. After loading comes at the top "importing …".

- is/are an folder/folders
  You can download an mod from Planet Minecraft when you go on your mod and say download. Then you must go in the file explorer.
  Say unpack and unpack the zip folder under %localappdata%\Packages\Microsoft.MinecraftUWP_8wekyb3d8bbwe\LocalState\games\com.mojang . And      then under development_skin_packs / development_behavior_packs / development_resources_packs . Then go in Minecraft and you have your mod/resources   pack/skin pack.