The Easy Way
Many of the trackside banners here on the site are supplied in PDF format, so they are quite simple to print off.
There are generally seven to each page, and they are designed to be printed onto an A4 sheet. If you print at full size, you'll find that the banners are 190mm wide, but there are cut lines to allow you to trim them down if necessary.
The Flexible Way
For those of you who want to put together a customised mixture of files or sizes, then there are PNG, and SVG files.
These should load into most word processors, or graphics applications.
The Creative Way
For those who want to change the colours, or sizes, or any other aspect of the graphics, then the SVG files are completely editable using Inkscape, a free vector graphics editor.