Thanks for the leads on purchasing bobbins and the foot. Here's a definition of vertical and horizontal...
Machines come with either a "horizontal bobbin" or a "vertical bobbin."
The horizontal bobbin is normally a "drop in" bobbin -- when you slide the needle plate over, you'll see a circular depression in which you "drop" the bobbin. There's normally an angled slot you'll pull the bobbin thread through.
A vertical bobbin requires that you use a bobbin case. You insert the threaded bobbin in the case, pull the thread through an angled slot in the case, then press the bobbin case into a slot under the needle plate. There's usually some sort of door covering this slot -- although older machines like Singer 301s and Featherweights have the bobbin case simply sitting underneath the bed.
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