Insufficient disk space on my Macbook Pro, unable to delete or move items

I have a 2012 Macbook Pro that is down to 309MB of space. I cannot move or delete anything. I cannot open iCloud. I shifted some items to an external HD, but cannot delete them off my laptop to start freeing up space. I am paying for 2T of iCloud space. Literally, the only thing I can do on my laptop is open my Downloads folder and copy the contents to an external drive. I need Help!!

[Re-Titled by Moderator]

Original Title: out of space on my HD. Cannot delete items or move anything to make space