Select Print from the Block menu to print the selection portion of the current file, rather than the entire file. A preview of the printout will be shown first. It will allow you to make some changes like which font to print with, which pages should be printed. You can also access the printer setup through the preview window.
There are two key differences between selecting Block|Print in the menu, versus selecting File|Print and turning on the "selection only" in the print preview. The checkbox works at the level of a single line. If a line is partially selected, it will be printed entirely. Block|Print, however, sends the exact selection to the print preview, and ultimately the printer. If you want to print a rectangular block, Block|Print is definitely more useful.
Syntax coloring will also be printed differently. Since File|Print sends the whole file to the print preview, the printed lines will be colored the same whether you're only printing the selected lines, or you're printing the whole file. Block|Print only sends the selection to the print preview, and the syntax coloring will treat the selection as if it is a complete file. If your selection cuts through syntactic elements, they won't be colored properly in the printout when using Block|Print. In that case, you can turn off the "syntax coloring" in the print preview to print without syntax coloring.