This isn't as intimidating as it may sound. Machine in this case just means a computer and printer, or a photocopier. The idea is to simply use one of these devices to print your pattern directly onto a transparency.
Office supply stores usually sell transparencies designed to work with various printers. You want to use the correct transparencies/acetate with laser printers, if you use a regular acetate, it will melt in the printer. This is a low quality method to create film positives.
Good quality film positives can be obtained by using ink-jet printers. If you combine a dye ink Epson printer such as the Epson Stylus 2400 with the correct films such as AccuBlack or AccuArt the results are fine for commercial screen printing. For good results you are looking for high opacity and a high contrast between the film and the ink laid down.
Alternatively, many copy shops should be able to copy a pattern onto a transparency. This may be quick but the opacity is low. Between laser printers or paying a copy house to do it, I don't know which is more expensive in the long run.
Which ever you choose to use, make sure the image is going to block out enough light. Typically, this kind of printing or copying is intended for over head projectors which don't actually require very opaque images. You can try printing a sample to see how opaque it is. If you've done a lot of photo emulsion stenciling, you can probably get a good idea just by looking at it against the light of whether or not it's dark enough. If you're not sure, you can experiment with it, and just be prepared to waste the stencil if it's not dark enough, or you can maybe waste a little money and play it safe. There's a few things you can do to make it more opaque. First, if you're at a copy shop, ask the clerk for suggestions, they may have special toners that are more opaque, and they can probably increase the contrast to make a darker image. If you're printing at home, you can play with your printer settings to try making the image darker. An alternative for either copier or printer is to do double copies of all your positives, and just make sure they're well lined up before using them on your screen. You can use clear acetate desk tape to fold them together since it won't block any extra light. You just have to be real sure you get them lined up right or your image will end up kind of funny. You could also increase opacity by "double siding" a machine printed original, as described above.