How do I custom position default login form that (in my case with BLUEMASTERS theme) pops up down below the title of the content page like: ABOUTUS. I want to position it in the sidebar.
Go to "Blocks" under "Structure" (admin/structure/blocks if I'm not wrong). You'll find the "User Login" block and you can position it where you want, depending on the theme you have. It might be named "Sidebar" or "Sidebar Left (Right)" or "Sidebar First (Second)".