So English is not my first language , bu I will try to do my best.
To complete this project we need to create a board model this model will have an array with Threads, this Threads is also a model will an array of replies , replies is also a model.
Thread model, and reply model sound right. If you’re making multiple boards, a board model would be useful as well. Think about how your data is going to look; a thread could be a json object with multiple fields. If there are meant to be multiple replies for, say, a ‘replies’ field, you could store them in an array. Each reply itself could be represented as a json object. It would be called a ‘document’ in a document database such as MongoDB. Documents make up a ‘collection’. For example, you could have a collection called ‘users’, and each user would be represented as a document. You would need a ‘User’ model to create individual documents. It’s often best to think about these projects from a data point of view. Make it easy on yourself by using Mongoose.