I have to create this folder named "files" in uploadtemp folder:



If I currently in :

davy@ubuntu:~$ ls
core Documents examples.desktop Pictures Templates
Desktop Downloads Music 

how to create that files folder?

Well, in general, *nix usually has a forward slash (/) delimeter, not a backslash (\).

From your current position you would do:

mkdir /red5/webapps/openmeetings/uploadtemp/files

Of course, you need permision to create that directory. If you do not have permissions you need to do the action as root or with elevated priveleges (sudo).

Also, if any of the intermediate directories don't exist, you can add the -p option to mkdir. IE,
mkdir -p /red5/webapps/openmeetings/upload/files

This is what happens:

davy@ubuntu:~$ sudo mkdir /red5/webapps/openmeetings/uploadtemp/files
[sudo] password for davy:
mkdir: cannot create directory `/red5/webapps/openmeetings/uploadtemp/files': No such file or directory

Did you try rubberman's suggestion of including the -p flag?

Does /red5 or any of the subfolders your reference even exist?

davy@ubuntu:~$ mkdir -p /red5/webapps/openmeetings/uploadtemp/files
mkdir: cannot create directory `/red5': Permission denied

You need to be root in order to create directories at that location, so you need to use sudo at the beginning of the command.
sudo mkdir -p /red5/blahblahblah..............