Create a struct named Post with three stored properties:

It seems that the struct Tag is needed for the struct Post and not the opposite. To access a struct within a struct, you need to access it via the first (i.e.: Post.Tag). Also, be sure to close all your brackets. and I don't think that you cannot init a struct wihin the struct itself because it will be not initialized first.

The following code works in playground without errors:

struct Post {

struct Tag {
    let name: String
}
let title: String
let author: String
let tag: Tag

}

let firstPost = Post(title: "a string", author: "a string", tag: Post.Tag(name: "aTag"))

Just move the instance out of your Struct Post

struct Tag {
    let name: String
    }

    struct Post {

        let title: String
        let author: String
        let tag: Tag

    }

let firstPost = Post(title: "Yes", author: "Jim Toms", tag: Tag(name: "Emtpty"))

you are close, all you gotta do is move your instantiation of Post out of the definition of the Post struct. just cut and paste it below the closing curly brace of the Post struct and it will pass.