Assuming I understand what you mean:
-
If your
UserControl
is in a library you can add this to you Toolbox usingToolbox -> right click -> Choose Items -> Browse
Select your assembly with the
UserControl
. -
If the
UserControl
is part of your project you only need to build the entire solution. After that, yourUserControl
should appear in the toolbox.
In general, it is not possible to add a Control from Solution Explorer, only from the Toolbox.