Hi
In the network section, there are many networks. For proper functioning, do I necessarily have to connect to all the networks? If I connect to all the networks, am I at risk of using too much bandwidth? If I connect to only one network, will I get unsatisfactory results in my searches?

You can read some documentation, the link is above.

“Network” is just someone being online and organizing service for a group of people. Can be topical or general, public or private. Almost no traffic is used when client is idle.

With current number of users, there is not much difference in choosing groups, public files are provided by only a dozen of people. Treat DarkMX as a private sharing solution that does not depend on corporate servers.

Thank you for your kind response, but I still haven't been able to understand how it is convenient to set up the connection to the groups.
I have used many P2P programs, starting from WinMX, and generally it was important to connect to the server with the largest number of users or, as on eMule, there was a way to search even on servers you were not connected to. What matters to me is the search results.
Let me give you an example: if I connect to only one group and the user who has the file I am interested in is connected only to another group, will I get that file as a result of my search?