I have two sets of layers in this graph, one for letters and one for paths, is there any other way to quickly select this set of letters by excluding layer selection? Figure 2 shows my habit of using FREEDHAND to use one-click selection.

I'm not sure that I understand your question. Hopefully this helps.

Inkscape's canvas tells you the active layer or group for editing operations, layer "0" in your case. [ctrl+a] selects all objects in this layer. [double_click] a group to open it (i.e. make it the active scope) and then [ctrl+a] selects everything in that group. The [Layers and Objects] dialog can select objects across multiple layers and groups without changing the active scope in the canvas.

Also helpful settings:

You guys should not understand what I mean. My case is that the letters are a group, the path graphics are a group, and they are a group in general. I am trying to click on a letter to quickly select that letter group. Your method should select this overall group.

[double_click] one of the text objects repeatedly to drill down through the nested groups. When your selection contains a single text object, [ctrl+a] selects all the objects in the parent group. Here's a hypothetical document structure:

   Layer 0
      overall group
         text group
            symbol 1
            symbol 2
         path group
            path 1
            path 2
            path 3

initially "Layer 0" is the active scope
[ctrl+a] selects "overall group"
[double_click] "overall group" to open (activate)
[ctrl+a] selects "text group" and "path group"
[double_click] "text group" to open (activate)
[ctrl+a] selects "symbol 1" and "symbol 2"
[double_click] outside a group to activate the parent group or layer

I didn't quite understand what you meant before, and I tried for a long time. Finally I know how to operate, thank you very much.