<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/imagem_teste" />

<Button
    android:id="@+id/bt"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal"
    android:backgroundTint="@color/viewfinder_laser"
    android:text="Entendi"
    android:textAppearance="@style/TextAppearance.AppCompat.Large.Inverse" />


</LinearLayout>

btnSobre.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                LayoutInflater li = getLayoutInflater();
View view = li.inflate(R.layout.alerta, null);

                view.findViewById(R.id.bt).setOnClickListener(new View.OnClickListener() {
                    public void onClick(View arg0) {
                        alerta.dismiss();
                    }
                });

                AlertDialog.Builder builder = new AlertDialog.Builder(TelaInicial.this);
                builder.setTitle("Sobre...");
                builder.setView(view);
                alerta = builder.create();
                alerta.show();

            }
        }
);

AlertDialog.Builder builder = new AlertDialog.Builder(TelaInicial.this);
            builder.setTitle("Sobre...");
            builder.setView(view);