通常每个Activity对应1个Layout，在onCreate时指定layout（否则引用的还是main的layout）,然后调用startActivity：

protected override void OnCreate (Bundle bundle)
		{
			SetContentView (Resource.Layout.UserRegister);
			base.OnCreate (bundle);


			// Create your application here
			var btnBack =  FindViewById<Button> (Resource.Id.btnUserRgst_Back);
			btnBack.Click += (object sender, EventArgs e) => {
				StartActivity(typeof(MainActivity));
			};
		}

如果要传值，可以使用intent：

var intent = new Intent(this, typeof(UserRegister));
				StartActivity(intent);