KDE comes with the console application Konsole. You will usually find it in the start menu in . If you do not have a full KDE installation any console application, such as xterm will do just fine.
When asking for help you may be told to "open a console" or "open a terminal" - they are the same thing. Why would you want to? Well, sometimes something doesn't behave as expected. When you use a GUI (graphical user interface) to do something, you don't know why it failed. If you open a terminal and try to do the same thing from the command-line, you will get a lot of text showing while the command is working, and what it reports will help people to help you find the problem.
There are several ways, and the one that is easiest for you depends in which distro you use. It's very likely that in your menu you can see an entry with an icon that looks like a black, blank screen, like this: or this . Click on that and your console will open. Just type in the command your helper gives you, tell your helper what happens.
If you can't see the icon, is there a search box in your menu? If so, type
konsole there. That is KDE's console. If that isn't found you may not have KDE installed yet, but there's no problem.
xterm can be typed instead and you are sure to have that installed.
If you do have KDE installed you might like to try Alt + F2. This opens a small window where you can type the application name -
|if your helper tells you to open a console, take care not to introduce upper-case letters unless you are told to. In Linux, unlike Windows, everything is case-sensitive. If you introduce an upper case letter where there should not be one, it won't know what you mean, and will probably tell you that there is no such file.|
Later, as you gain confidence, you may find that you use a terminal more often, as some things are much faster from a console, but you needn't worry about that at first.