do you mean using blocks you created yourself?
if so,
You may set part library to your folder (default: /usr/share/librecad/library in linux) by main menu: Edit -> Application Preferences -> Paths -> Part Library
Your folder may contain sub-folders with your blocks/dxf files.
Then, Main menu: View->Tool Bars -> Library Browser
You can insert blocks there.
Johnson wrote
Dear Folks
I want to customize some picture into a group by using block menu ?
Next time I open LibreCAD I could use those block to draw objects directly .
Could someone tell me how to use those menus ?
Thanks.