have created a sidebar called “Blog sidebar”
general points to check:
do you have the sidebar registered in functions.php?
http://codex.wordpress.org/Function_Reference/register_sidebar
do you call the sidebar from your template?
http://codex.wordpress.org/Function_Reference/get_sidebar
have you created a new sidebar file matching the call?
what file name does this sidebar file have?
what is the content of this file?
for specifics, please contact themeforest as the seller of your theme ‘dandelion’ for support; this is part of what you pay for when you purchase a theme.
apart from general suggestions, this forum does not support commercial themes.