The left one has two hands, the right one has two hands with a 口 in the middle.
In ancient time, people hold two hands together to greet each other.
The 口 in the middle is a big square where people get together for sacrifice, all greet each other by holding both hands in front of the chest.
The greeting had changed a little bit to become holding both hands together a few hundred years ago.
Don't be confused with greeting among people who do Kung Fu.
which is one palm and one fist, a specific greeting between Kung Fu masters because they use fists and palms.
The big seal script for Together is
The small seal script for character Together is
The clerical script of the character is
Its song typeface is
Almost same as clerical script.
Its Pinyin is Gong4.
共 emphasizes doing something together, not just stay together. It also means Common, or All.