ANSI Mouse gives you a text editor with a bunch of weirdo extensions (as you may be able to tell already). As long as you're using the TEXT TOOL (click on the letter 'A' icon on the tool dock) the editor will behave as described below.
The editor is always in 'replace' mode. It will always write over what is already there when you type. If you want to insert a word, you must hit Ctrl-I to move the existing text to the right. Here's a short summary of the main editor keys:
Command-I - Insert in the current line
Command-D - Delete character at current position
Command-J - Insert line before current line
Command-K - Delete current line
Clicking - move to that coordinate
Arrow keys- move the cursor in that direction
The text style can be changed by making selections from the Text menu or pressing the follow keys:
Command-P - Plain text
Command-B - Bold text
Command-U - Underlined text
Command-R - Reverse video text
The text styles are additive, so you can have both bold and underlined at the same time, for example. If you set it to Plain, however, it resets everything. You may also select the text styles by clicking on the tool bar in the proper location, but there's more on that later.
Text color may also be changed. You may set the fore- ground color by selecting from the Foreground menu on the Text menu, or pressing Command-1 through Command-8 to select that color. Background colors may only be chosen from the Background menu on the Text menu.