You can edit files from the Working Copy View by double clicking them or by right clicking them and choosing Open from the popup menu, or from the Synchronize View by using Open from the popup menu. Please note that only one file can be edited at a time; if you try to open another file it will be opened in the same editor window. The editor has syntax highlighting for known file types, meaning that a different color will be used for each type of recognized token in the file. If the selected file is an image, then it will be previewed in the editor, with no access to modifying it.
When you edit a file from your working copy, you will notice that after modifying and saving it, a modified marker - an asterisk(*) - will appear on the file's icon in the Working Copy View.