glN64 0.4.1. How do i show FPS in full screen & 32bit or 16bit?

1st q: not possible. The only plugin to have this option is glide64.
2nd q: the option is there because it's drawing the gfx with direct3d. In other words, it doesn't emulate the color, but writes it directly on the monitor. For n00bs, this means that it's just a simple option that controls how stuff looks on your monitor.

To see the frames per second (not fields per second or VI/s) download fraps www.fraps.com

The N64 uses 16-bit color. The option is there in glN64 because you can get higher quality results using 32-bit color, and since it's just HLEing the N64's renderer, it doesn't matter that the bit-depths don't match up.

You'd rarely want to set it to 16-bit since there is nearly no speed difference between 16 and 32-bit color on today's GPUs, and the graphical quality is much higher in 32-bit.

As far as i know it's 24 bit(!!!)
Like top gear rally"paint shop", you can chose between 256 positions on RED, 256 positions on GREEN and 256 positions on BLUE, so logical 256 color= 8 bit x 3 channels (green red and blue)= 24 BIT COLOR!!!
Or to explain better: it's like 32 bit color, but it's RGB, so it doesn't have the opacity channel for 32 bit,but it's LIKE 32 bit.
16 bit = 65536 colors
24 bit =16.777.216 color (256x256x256)("little" diference, huh?)