Select Uncomment from the Block menu to remove the comment characters added by Block|Comment. When you've made a selection that flows with the text, Block|Uncomment will remove the comment characters from the very start of the line only. Comment characters in the middle of a line are left. When you've made a rectangular selection, only comment characters starting at the first selected column will be removed. Comment characters at other columns are left.
If the syntax coloring scheme does not define opening and closing characters for comments, Block|Uncomment will try to remove the pair from the start and the end of each line when the selection flows with the text. When making a rectangular selection, it should include both the opening characters and closing characters on each line. Only comment characters inside and at the edge of the selected block will be removed.
Though Block|Uncomment requires you to be a bit precise when selecting the block to be uncommented, this makes it possible to comment out blocks that already have comments in them, and then uncomment those blocks while leaving the original comments.
If you did not select any text before using the Block|Uncomment command, or the selection does not span more than one line, Block|Uncomment will attempt to remove comment characters at the very start of the line containing the text cursor. Whether any comment characters were removed or not, it will then move the text cursor to the next line. If you've assigned a keyboard shortcut to Block|Uncomment, you can quickly uncomment a bunch of lines this way.