1) Show only files with a special extension:
Use *.extension as filter. "*" replaces all filenames and ".extension" is to be replaces by your extension. For example if you want to show only mp3 files, use this as filter:
*.mp3
If you want to show only mp3- and wav-files, you can seperate both with a semicolon:
*.mp3;*.wav
More examples:
image filter: *.jpg;*.bmp;*.png;*.gif
audio filter: *.wav;*.mp3;*.wma;*.ogg
video filter: *.mpg;*.wmv
2) Show only files beginning with a special letter
That is what you have to use as filter: yourletter*.*
For example if you only want to see files beginning with an "a", use
a*.*
as filter. You can also combine with an extension, so using
a*.mp3
you will only see mp3-files beginning with "a". Again you can combine multiple elements with ";".
Tip: You can also use "?" instead of "*".
"*" replaces an undefined number of chars, "?" only replaces one letter. So if you only want to see all files with "a" as first letter and any second letter use
a?.*
Files like ab.mp3 will be displayed, however no files like abc.mp3.
in toolbar.
you find at top right in CD layout. CDBurnerXP Pro will minimize and only leave a small box at top left corner which you can move. Now you can explore your PC (Windows Explorer) and drag your files onto the box to add them to compilation.
erase feature instead. Alternatively you can use the "Clear"-Button in middle toolbar. 
Move one folder upwards
Create a new folder in the folder you are currently browsing
Select all files of the current folder
Deselect all files of the current folder
Invert current selection, all files that were selected are unselected, and all files that were unselected are selected after pressing this button.
Filter the files that are shown. Here is how it works:
