First of all, you need to learn standard core Ruby, before you can effectively use the SketchUp API which extends Ruby for use with SketchUp. Ie, The SketchUp API documentation is not a teaching document, it is a technical reference.
See my wikilist, in this category for resources:
… which lists:
Read this on how extensions should be organized for the Extension Warehouse (or generally valid for the SketchUcation PluginStore, but they may have a few different rules):
This kind of question is best asked more specifically, by posting a specific code snippet, so readers know what your asking about. The way it is now some reader would need to be intimately familiar with this specific plugin. Also, when speaking of a particular plugin, give a link to it’s GitHub repo, or EW page, etc. If it is only a posted example, give the link to the forum thread in you question post.
So I and other readers are not interested in hunting down what it is your speaking of. You need to understand that there are thousands of plugins, and tens of thousands of code snippet postings on the web.
Correct. This dialog panel is for toggling extensions once they are already installed.
Browse, Install and Uninstall are features of extension / plugin store extensions. (Trimble EW, SketchUcation PluginSotre, etc.)
Yes IF you have opened the EW from INSIDE SketchUp, and it is loaded in a child browser frame, you can browse, install, update and uninstall, from this child browser window.
But not if you open the EW website in an external browser.
This question is unclear. IF you are asking if you can uninstall in multiple ways, then yes. If extension manager extensions have a uninstall available for a installed extension you can use it.
However there may be limitations. The EW may only be able to uninstall those extensions that it itself had installed. The SkecthUcation PluginStore extension may also have the same limits. (You’ll have to read the instructions.)
If you manually install an extension, then eventually you may need to uninstall by manually deleting the extension registrar script and it’s extension sub-folder (which usually have the same name.)
It identifies each particular extension and it’s current version, to the Extension Warehouse server.
This is needed for notifying of updated versions, license management (for paid plugins) and for uninstalling, etc.