Quickstart

Create a form class, with which the application should start with. It has to derive from Form.
Use its constructor to set up the various properties, like Content, Size, Title, Icon, and more.

class MainForm : Form
{
    public MainForm()
    {
        this.Title = "Demo App";
        this.Size = new Vector2(700, 400);

        // ImGui.Forms uses imageSharp for its internal operations and image buffers.
        this.Icon = Image.Load<Rgba32>(@"path/to/icon");

        this.Content = new Label { Text = "Demo Text" };
    }
}

Create an instance of Application and let it show your main form.

var app = new Application();
var form = new MainForm();

app.Execute(form);

Voila. You have created and started your first application with ImGui.Forms.

For all the components and how to use them, refer to Components and Layouts.
For a more in-depth look at Application and Form, refer to Application.