WorldEdit Betas are versions of the addon with unfinished features that will likely be included in full releases. By using Betas, you can help to report undesired behaviour, i.e. bugs, and give feedback on the very latest features of WorldEdit. Being a more unstable version of WorldEdit, it's not recommended to use Betas in worlds you care about, unless you make a backup of them.
Unlike the release versions of WorldEdit, betas don't come as a packed .mcaddon file. Instead you'll get two folders containing the behaviour and resource packs. You must take these two folders, and move them to two other folder within your game's com.mojang folder, development_behavior_packs and development_resource_packs respectively. The location of com.mojang depends on your device. Once you moved the folders, you're free to add the packs to worlds you choose to test the addon in. Betas have [DEBUG] at the end of their name.
Betas are in debug mode by default. In this mode, more types of messages will appear in the content log. But to see the logs, you'll have to enable it as described in CONTRIBUTING.