I actually know this one! It depends on how the thread is put on the spool. If the thread is in the spool straight then the thread needs to come off the spool straight as well you would position that spool upright. If the thread crosses in a V pattern, the thread is meant to come off from above it so you can either use a cone holder and have the thread on it or load the thread sideways so it pulls it over the top of the spool.
Originally Posted by QBeth
I found some photos so I hope they help explain this too.
Example of a spool that needs to be upright
Example of a spool that needs to be sideways or on a cone thread holder