Please analyze me the use of bars in the explorer table in roblox studio ?

If I understood the question correctly, so here's the answer. These things you see in the explorer are not called "bars". They're name in Roblox Studio is "Services". Each of the following services does something different. For example, the StarterGui is a service that controls all about the UIs in the game, otherwise the Workspace is controlling everything about the game's environment, like characters, parts, and more. There are a lot of services which you don't have access to by the normal explorer. Here are some examples : Visit service, notification service, tween service, and a lot more. To access these services you'll have to use GetService() function, here's an example:

local Service = game:GetService("Visit") --This following code defines the Visit Service.

Learning all the services is not so recommended as a beginner. You should first learn the most common services like StarterGui, Workspace, TweenService, NotificationService, StarterPack, StarterPlayer. Then when you're an expert in each of them you can learn some extra services like Visit Service etc. So, these are the "bars" in the explorer. I hope it was helpful!

Usually, you would use GetService on any of these. While not all objects in explorer require GetService, it is good practice to use it. For example:

local service = game:GetService("MarketplaceService")

When you get a service, you are getting all the functions of that service. That is why everybody uses GetService.