B5c configuaration, and what channel best to choose

what does (1x 40 MHz FD) means in channel width in b5c and (DFS) in frequency mode. thanks

FD is frequency division. Basically one radio transmits on one frequency and receives on another. This is to help with high interference on both radios but each radio has a different channel that is somewhat clean or available.

DFS is Dynamic Frequency Selection. DFS channels are those used by radar around the world. Using a DFS channel means you transmit at lower power and, if the radio detects a radar signal, it has to change to another channel.