From the assembly editor menu, please select File -> New. BW Tools will display a dialog asking for a template. Using the combobox "Type" switch to "Outfit". The list box contains a list of available templates.
Double-click on "Business Shirt with Tie - Men's" to select it. The assembly editor will load this template into its editor pane and do an automatic "Refresh". You should see a wireframe body with a shirt. Left click and drag to inspect it. Use the middle wheel (or the up and down keys) to move it closer or away. Double-click to return to the initial view.
Let's make a change to this outfit. Find the subpart name "_Shirt". Change the PAINT statement from
PAINT DIFF 1 0 0
Do a "Refresh!" using the menu.
Select File -> Create As to create and save the final outfit. But caution: This will not save the assembly text itself! If you wish to save the text, select File -> Export Text...