@mks: Why do you want to type a command to create a directory?
Use Files > New > Directory.

Or are you actually trying to automate something? Do you want to write a script?
Then start here: https://winscp.net/eng/docs/guide_automation

Maybe you should actually explain us your overall task, rather than asking for tiny details. Because chances are, that you are on a completely wrong track.

@Pathduck: But what if I want e.g. to create a directory on the remote site?

Well,
Ctrl+T opens a terminal window
Ctrl+Shift+N show the command line.

But neither of these allow the entering of FTP commands I think, they are for shell commands. Maybe if you change the advanced connect properties to use another shell.

This is the charm of WinSCP, you do not need to type commands, you can use F5 for copy and so on, or drag-and-drop if you want :)

Please kindly excuse me for asking newbee questions. My problem is essentially: how could I, starting from a normal window of WinSCP, enter an FTP command, i.e. which button I must first click on in the normal window in order that I could obtain a tiny window in which I cound enter an FTP command?

What screenshot? The one from my post? What is on the bottom there, is a transfer queue. That has nothing to do with command-line. You do not need that.

But how can I come to what is shown in the screen shot, i.e. which button I must click in order to have what is shown in the screen shot? (I don't have initially what is at the bottom.)

There's Options menu:
https://winscp.net/eng/data/media/screenshots/commander.png

I read "Command line is an optional component .... To show/hide the command line go to Options > Command line. But I don't see the Options button.