Quite a beginner's questions

[Deleted member 30996]

Now I'm going to have BSD as my desktop.

I've had FreeBSD and OpenBSD desktops. FreeBSD feels more polished as a desktop OS to me. I've switched all my other boxen over and have 9 laptops running FreeBSD.

Here's something you may find of some use. You already know how to use a terminal so you can disregard those parts but still follow the outline to get to the desktop. You can use pkg instead of ports but you have to consult the Handbook and it's only a few commands:

Beginners Guide - How To Set Up A FreeBSD Desktop From Scratch

I'm going to guide you though the process of getting a fully functional FreeBSD 13.0-RELEASE desktop up and running, complete with system files and security settings, step-by-step as if you've never used UNIX or the command line. Now let's get started: Insert your boot media and at the Welcome...

forums.freebsd.org

 

[astyle]

I am an IT specialist (translating from a translator) and it seems to me that it is a matter of time until someone tells me to configure a firewall on BSD, so I need to know some BSD distribution.

I'm an IT specialist myself, and English is my second language, as well. Linux has iptables, FreeBSD has ipfw, OpenBSD has pf. Windows has Windows Firewall. For a 'home' connection, your router/modem will also be your firewall. Quite frankly, correctly configuring a firewall has very little to do with choice of the OS. You gotta know where on the network you set it up, and what you'll let through or reject. With those basics firmly in mind, you can pretty much pick something at random, and set it up to achieve the exact same results.

 

[fel1x]

I don't know which distribution to choose:
-FreeBSD seems to have the best documentation.
-OpenBSD is said to be the safest distribution.
-DragonFlyBDS seems interesting to me.

Try FreeBSD if you are not familiar with BSD.
NetBSD is appropriate for non x86/amd64/arm/aarch64(Additional Information: From FreeBSD 13, it support RPi4 finally!)
I don't no much about DragonflyBSD, but I heard it is based on hybrid kernel and uses HAMMER2 file system.
OpenBSD is the safest one in terms of security, and it also has the least codes.(Normally, the amount of code and the level of security are directly proportional.)

However, the most important thing is that the reason why you want to you BSD.
For firewall, servers(etc. mail server), and embedded systems, FreeBSD is much better than Linux due to its stability and it is smaller than Linux. But in the case of general uses like games, I recommand Linux or Windows(Windows is only better for games and Adobe things.) because you can find more references on Linux than FreeBSD.

It is your choice to choose what BSD or Linux. There are somethings that are hard to tell by words because everyone's preference is different. Some people pursuit simple systems, whereas some people prefer high-performance systems. Experiencing all three BSD will be a valuable experience, and it can help you what BSD to decide or recommend to your friends and colleagues.