I have a Cameo but will try to help
1. Watch this video by Gina K. She is setting up the Cameo but I think the blade goes in the same way on the Portrait. The numbers on the blade cylinder are on the bottom and there is a ridge that protrudes on the upper side of the blade cylinder that must go into the slot. First you need to release the blade lock, by turning the blue knob counter clockwise. Be sure to turn the lock back when you finish.
SIlhouette Cameo - Getting Started - YouTube
2. If it is not cutting the blade may not be set to the proper depth. Check on the right panel in the software and it tells you the correct settings for various material . You need to choose vinyl to get the correct settings for that
3. The reason you can't get the vinyl to fit between the rollers is the Portrait only cuts a maximum width of 8" and the vinyl is 9" wide . You will need to trim the vinyl by at least an inch so it will fit between the rollers
The Cameo cuts 12" wide material
4. Scroll down here to download the complete Silhouette Studio manual
Silhouette - Download New Software
Hope this helps
Barbara