Across the overworld, you'll find randomly spawning Monster Dens, which are randomly generated and will include a nest from which you can gather eggs that you can bring back to town and hatch. In practice, that means stealing their young, too. If you're not already familiar with Monster Hunter Stories' main gameplay loop, the name of the game is working together with monsters instead of just mercilessly slaughtering them.
An expansion on existing ideas and frameworks, rather than a complete rewrite. While Wings of Ruin makes a number of changes to improve the experience, fundamentally they're both very much the same type of game at their core. As you might've gathered, Monster Hunter Stories 2 is the iterative sequel.