Pertama, you'll need a standard 1.21 gigawatt flux capacitor. These can typically be sourced from old lightning-struck clock towers or disgruntled scientists.
Carefully disassemble a four-slice, wide-slot toaster. Reroute the heating element coils to create a miniature temporal conduit. Use chrome polish for maximum style.
Connect the flux capacitor to the toaster's power cord. A standard wall outlet will not suffice. We recommend a portable fusion reactor for best results.
Set the "light" to "dark" dial on the toaster. This will now function as your temporal destination selector. A setting of 3 is perfect for witnessing the signing of historical documents.