Active is the visible resolution.
Blanking is the period between each line (horizontal blanking) and each frame (vertical blanking). This was originally intended to give CRT monitors time to move the electron guns. LCD monitors don't need as much time, so the blanking can be reduced.
Blanking = front porch + sync width + back porch
Front porch, also known as sync offset, is basically padding before the sync pulse.
Sync width is the duration of the sync pulse. The sync pulse marks the start of the next line (horizontal sync) and the next frame (vertical sync).
Sync polarity is whether the sync pulse voltage goes up (+) or down (−). Most monitors can handle both.
Back porch is basically padding after the sync pulse, before the start of the active pixels.
Total is the total number of pixels including blanking.
Total = active + blanking
Frequencies
Refresh rate is the number of screen refreshes per second.
Horizontal scan rate is the total number of horizontal lines per second including blanking.
Horizontal scan rate = vertical total × refresh rate
Pixel clock is the total number of pixels per second including blanking.
Pixel clock = horizontal total × vertical total × refresh rate
See also: Common pixel clock limits
What timing parameters should I use?
Use whatever works. Standards exist to make sure certain values always work so devices can operate with each other, but if you're trying resolutions or refresh rates that the monitor doesn't officially support, there's no guarantee any particular timing parameters will work.