Here are a bunch of tutorials for manufacturing small to medium scale (10 - 10,000) piece surface mount electronics.
736X736mm SMT Frame for SMT Stencil in PCB Assembly Production Line - China Stencil Frame, Pneumatic Frame
Hot Sale NeoDen SMT Solder Printer SMD PCB Stencil Printer Manual Solder Paste Printer FP2636 Support Framed Stencil - AliExpress
SMT Stencil in JLCPCB Factory - EasyEDA open source hardware lab
PCB Stencil Guide From Basic Concepts to Design Details-FS PCBA
584X584 Framed SMT Stencil manufacturer from China
SMT Stencils – Agile Circuit: PCB Manufacturing & Assembly Service Supplier in China
stainless steel PCB stencil Manufacturer, For Industrial, Packaging Type: Box at best price in Pune
SMT stencil - definition and different types - IBE Electronics
Printed Circuit Board SMT Stencils