How can I create torrent files from transmission or deluge using GUI?

With Transmission, it's pretty simple. Go to the File menu, click on New:

Choose the file/folder you want to share in the Source Folder/File options and the location where the torrent file will be created in the Save to option. Add any trackers and comments, and click on New. You will be given an option to add the created torrent to Transmission.

In Deluge too, the process is simple. Press CtrlN, or, in the File menu, click on Create Torrent:

When you click on Save, you will be asked where to save the new torrent file.