How to fix these errors?

Are you going to tell us what the warning is?

And what version of Xcode you are using (compared to the one Paul Hegarty is using, in the Demo you are working from)?

Do you mean those warnings ?

        if emojiCount > 1 {
// here's the first error which says "Cannot find 'emojiCount' in scope'"
            emojiCount -= 1
// here's the same error which says "Cannot find 'emojiCount' in scope'"
        }

You're new to the forum, so welcome. And get a few advices:

• You'd better expose error messages clearly and not let others search for them in code…
• when you post code to avoid leaving 20 blank lines… Use Paste and Match Style and then code formatter tool. That will make your code easier to read.

I noted several errors:

    var emojis = ["🚲","🚂","🚁","🚜","🚕","🏎","🚑","🚓","🚒","🚁","🚀","⛵️","🛸","🛶","🚌","🛺","🚇","🚠","🦽","🚗","🚚","🛴","🛵","🚅"]

There need a space after =before [

var remove: some View {

is defined out of

struct ContentView: View {

Hence,

   @State  var emojiCount 

is not visible out of its scope (the struct).

Probably, you have a misplaced closing parenthesis.

This should be correct:

import SwiftUI

struct ContentView: View {
    
    var emojis = ["🚲","🚂","🚁","🚜","🚕","🏎","🚑","🚓","🚒","🚁","🚀","⛵️","🛸","🛶","🚌","🛺","🚇","🚠","🦽","🚗","🚚","🛴","🛵","🚅"]
    
    @State  var emojiCount: Int = 4
    
    var body: some View {
        
        ScrollView {
            LazyVGrid(columns: [GridItem(), GridItem(), GridItem()]) {
                HStack {
                    ForEach(emojis[0..<emojiCount], id: \.self, content: { emoji in
                        CardView(content: emoji).aspectRatio(2/3, contentMode:.fit)
                    })
                }
            }
            .foregroundColor(/*@START_MENU_TOKEN@*/.red/*@END_MENU_TOKEN@*/)
        }
        
        Spacer()
        
        HStack {
            remove
            Spacer()
            add
        }
        .font(.largeTitle)
        .padding(.horizontal)
    }
    
    // REMOVE HERE ---->   }
    
    var remove: some View { // Now, this is in ContentView scope, and emojiCount is in scope
        
        Button {
            if emojiCount > 1 {
                // here's the first error which says "Cannot find 'emojiCount' in scope'"
                emojiCount -= 1
                // here's the same error which says "Cannot find 'emojiCount' in scope'"
            }
            
        } label: {
            Image(systemName: "minus.circle")
        }
        
    }
    
    var add: some View {
        
        Button {
            if emojiCount < emojis.count {
                // here's the same error which says "Cannot find 'emojiCount' in scope'"
                emojiCount += 1
                // here's the same error which says "Cannot find 'emojiCount' in scope'"
            }
            
        } label: {
            Image(systemName: "plus.circle")
        }
        
    }
}  // <------- INSERT HERE
    

struct CardView: View {
    
    var content: String
    
    @State var isFaceUp: Bool = true
    
    var body: some View {
        
        ZStack {
            let shape = RoundedRectangle(cornerRadius: 8)
            
            if isFaceUp {
                shape.fill(.white)
                shape.strokeBorder(lineWidth:3).foregroundColor(.blue)
                Text(content).font(.largeTitle)
            } else {
                shape.fill(.blue)
            }
            
        }
        .onTapGesture {
            isFaceUp = !isFaceUp
        }
        
    }
    
}


struct ContentView_Previews: PreviewProvider {
    
    static var previews: some View {
        
        ContentView()
            .preferredColorScheme(.dark)
    }

}

Thank you very much Claude 31, I learnt a lot about forum rules and code from your reply

Nice to read. Did it solve your problem ? If not please explain what remaining issue. If solved, don't forget to close the thread (click the circle with the check mark in front of the correct answer).