In my designs from now on, I'll be providing links to Google drive uploads of the design's silhouette studio file, so for anyone else who uses the portrait 3, here's a brief general tutorial.
Download both the design and the silhouette file.
Open silhouette studio. Then open the silhouette file you downloaded by clicking "merge" under the "file" tab.
Make sure "snap to grid" is enabled under the "view" tab, and scale the design until it's 7.647 inches in width.
click the "Center to Page" button found at the top of your screen (it looks like a piece of paper with a gun scope in the middle).
Click the printer button and print from your printer like normal.
Click the "Send" tab on the upper right of your screen, click "Line", and make sure red is set to "Cut" and that orange is set to "Score"
Insert your printed design into your Portrait 3 and send it off!
I'll also sometimes include a sticky note in the silhouette file itself with more precise instructions or specific instructions for each model.