Does not understand the "Additional Generation Condition" structure procedure

Hello, I'm posting this problem since I haven't found a solution on the forum and on the Internet in general.
I would like to make an additional generation procedure to make the structure appear in my biome between a height of 60 and 65 blocks for example, that is to say not to make the structure appear outside this zone to avoid the mountains and follow the flat areas.

But I don't understand how this procedure really works.
Thanks for your help.