Depending on your setting, you either see a toolbar or a ribbon with many buttons. The buttons all show a tooltip explaining their function when you hover the mouse pointer over them.
On the left side of the window is a locator bar. This provides a quick visual reference as to where the changes lie within the file. The bar has three columns. The left column refers to the left pane, the right column to the right pane, and the center column to the bottom pane (if present). In one-pane view only the left column is used. The locator bar can also be used as a scroll bar to scroll all the windows simultaneously.
If you double click on a word then every occurrence of that word will be highlighted throughout the document, both in the main panes and the locator bar. Double click on the word again to remove the highlighting.
If you click in the left margin, or if you triple click within a line, that whole line will be selected.
Below the bottom window is the status bar. This shows the number of lines added and deleted in Theirs and Mine, and the number of unresolved conflicts remaining.
The status bar also contains combo box controls which indicate how the files are handled and treated:
The encoding specifies how the characters in the views are loaded/saved and shown. The most common encoding in English is ASCII (which means the local encoding of the OS language), but you can change this to be UTF8, UTF16LE, UTF16BE, UTF32LE and UTF32BE, both with or without a byte order mark (BOM).
The most common line endings on Windows is CRLF, but you can change the line endings to whatever you like. Note that if you change the line endings, then all line endings in the whole file will change, even if when loaded the line endings were not all the same.
The option at the top of the combo box menu indicates whether tabs or spaces are inserted when you press the tab key. The smart tab char option if enabled uses an algorithm to determine whether one or the other is best used.
The tab size specifies how many space chars are inserted when editing and pressing the tab char, or how many chars the next word is indented when a tab char is encountered.