That link I gave you has most of the indications to use selectors. Did you follow the tutorial?
In GC2, go to the selectors page, chose the selector you want, click on create, click on export. This creates a bitmap that can be used in Vue as a distribution map. It works very well but, of course, you may need to enhance the contrast of some of these bitmaps to have a good result in Vue. You can do this in a 2D program or in Vue itself (by attaching a node "brightness & contrast", for example, or others, like "quantize", etc).

The use of selectors is optional. You can use just the normal ways in Vue. Slope, height, etc. The selectors are good if you want to texture depending on some specific feature that Vue doesn't "know" about, like sediment or erosion (concepts Vue doesn't have when it comes to materials). Look at my image "Ascent". You see snow on the eroded parts of the mountain. That would be impossible to achieve in Vue alone because you have no control on Vue material editor about "erosion".

In GC2, I only use the special selectors, like sediments, deep flows, rivers, lakes, roads, etc. I don't use the other ones, like height or slope, because this also exists in Vue.

If you post some screenshots of where you're having problems, this could help diagnosis and give a more focused help.