How do I need to operate these functions to use them?

[xiaomashushu]

 

 

[Bryan]

These are additional settings for the mesh quality reduction. 
Normally, you do not need to use there unless you have issues with your exported mesh. 
Clicking on the (?) icon will display information about each function: 

[xiaomashushu]

Sorry, I didn't describe it clearly, actually I meant I can't use these functions. The selection box I can't select to enable these features.

[Bryan]

What Gaia version do you have? 

 

[xiaomashushu]

version：3.3.5

[Bryan]

Are you using Gaia Pro 2021 or the standard version Gaia 2021? 

 

[xiaomashushu]

Gaia Pro 2021

[Bryan]

Are you using a single terrain or multiple terrains? 

 

[Bryan]

So these settings are unlocked by changing the export preset to 04 Create imposters. 
Then you can change the imposter settings: