The OSDev Wiki Says

Alright I set DS to 0xFFFF, then enable the A20 Line, but I am not getting this,
DS as a base? The Segment:Offset is as follows (in my opinion)
0xFFFF:0x10, but how am I supposed to use DS as a base with that segment offset?

this is just 65520 bytes of memory above the 1meg limit which any real mode os can acess using 16bit segmented memory regs including cs so code can be run from there also

The segment represents bits 19:4 as a "base" and the offset is added on for bits 15:0; hence the linear address is "(base*16)+offset". Setting any segment to FFFF will mean you start at linear address FFFF0 and can add an offset of up to FFFF to reach 10FFEF if the A20 (i.e bit 20) line is enabled. (If A20 is disabled, this will truncate to 0FFEF.)