Choosing Browse > More > Search will enable you to find a pattern within the current file, the current directory, or the Inbox.
You are moved to the main window and asked this question:
Enter a string of characters and choose Browse. The search for the pattern will begin at the first line of the text file visible in the window and continue to the end of that file. The search is done ignoring upper/lower case-ness. A pattern of HELLO, Hello and hello will all achieve the same result.
If the string can't be found you will hear an audible error. If it is found, the pattern is highlighted in reversed colors. The command Again is added to the menu at the top with which you can repeatedly search again (beginning at the last place the pattern was found). If the search 'wraps-around' to the top of the file a unique sound is made to indicate this.
If the current view in Browse mode is not a file but a directory then a search will be made for the pattern through all the files in the directory (and recursively further down the hierarchy). A summary page is presented. You are shown all the lines where the pattern was found. You can elect to see each line within the context of the full file.
Searching for a letter in the Inbox (or the Trash/Inbox) acts in much the same way as a directory search.
If you choose Home or Done from the main menu at the top the Again choice will be removed. This is to prevent accidental searches of the entire Browse tree. You can always re-enter the search if you wish.