What do they mean when they say that u need a box tuned to so many khz, and how do u do this?

the sub im building a box for is the wooferjaycar 12' carbon woofer Power Handling: 300WRMS
Impedance: 4ohms (dual voice coil)
Voice Coil Resistance: 1.7ohm
Vas: 79.454Ltr
Qms: 3.238
Qes: 0.446
Qts: 0.392
Sensitivity: 88.152dB/Wm
BL: 9.992 TM
Fo: 28.77Hz
Sd: 514.720 sqCM

so how would i build a box for that woofer, they say to do a 28.3ltr sealed box

Basically when they talk about tuning, it is usually only for ported boxes. As far as I know, the only way to tune a sealed box is to vary the volume.

ok thanks