To connect a VGA monitor to the old DB 15-pin you need an adapter like the following:

Belkin VGA Adapter for Macintosh® computers F3H1381

Pasted Graphic 4

I found a manual online for the settings with the wheel and dip switches.

Settings for various computers:

Macintosh IIvx
512x384 Knob: 4; DIP ON: 5, 6, 8
512x384 Knob: 3; DIP ON: 8

Macintosh LC 475
1024x768 Knob: 1; DIP ON: 5, 6
1152x870 Knob: 4; DIP ON: 5, 6
800x600 Knob: 0; DIP ON: 5, 6, 8
832x624 Knob: 2; DIP ON: 5, 6

Power Macintosh 8500
1280x1024 Knob: 0; DIP ON: 1, 4, 5, 6