Interesting project, though it seems to be very very early in development, so I will give it some time to cook.You need to drag the egg from your inventory and drop it onto the terrain with the interaction/dialogue. After that, you can grow a new plant - and command it to grow tentacle-like roots to climb the canyon wall.
As for the lactation mechanic, it's unlocked through the story. It works like a power: in the world I imagined, the protagonist has (almost) full control over her body, so she can activate it at will - though, up until now, she never had a reason to use it.
But maybe this wasn't just visible from the few preview images, but it seems like lactation does not cause the PC's nipples to get darker and expand, now while this isn't the most important thing that the game needs right now, it seems odd if a game where pregnancy is going to be a major core feature needed to progress etc, not having one of the key changes that happens during a pregnancy seems weird to me.
Granted its new project etc, but at least an option to enable disable darker nipples would be appreciated in the future, especially if the character is some bio altered individual that has ''(almost) full control of her body, so having the ability to choose ones nipple color does not seem too unreasonable to me. (assuming all of this is in the game already)
Besides that, I wish you luck in development.