Combines several signals into one

Consists of

This alone allows us using the selectors, to choose which input

This is best shown with a 2 input multiplexer, which only needs 1 selector

in0 |---|
----|   |Out
in1 |   |---
----|   |
 sel  |
sel output
0 in0
1 in1

And thats all there is to it. This scales up with several inputs, several selectors, and one output