Here are the steps

1. dotnet add package Swashbuckle.AspNetCore
   • This will download and install all the deps.
2. Open your startup.cs file.

• Add in the ConfigureServices method

services.AddSwaggerGen(c =>
    {
        c.SwaggerDoc("v1", new Info { Title = "My API", Version = "v1" });
    });

• Into the Configure you will have to add

    // Enable middleware to serve generated Swagger as a JSON endpoint.
    app.UseSwagger();

    // Enable middleware to serve swagger-ui (HTML, JS, CSS, etc.), 
    // specifying the Swagger JSON endpoint.
    app.UseSwaggerUI(c =>
    {
        c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");
    });

Now you should be good to do a dotnet run and open the url https://localhost:5001/swagger/

More detailed guide can be found on the MSDN website and I recommend you to go and look.