The "window method" is perhaps the most common way to transfer a design onto fabric for hand embroidery. This method works best with light colored fabric, and can be used in conjunction with all sorts of transfer methods. I'll be using a pencil below, but you can also use a white water-erasable pen (e.g., for fabrics light enough to see through, but too dark for pencil marks), or any number of other transfer materials.
I've printed out a simple design onto normal computer paper to demonstrate the window method here, but you can actually also use this method by placing your hoop on top of your tablet or computer monitor (just be careful not to press too hard if you do this - you wouldn't want to damage your screens!).
This is known as the "window method" because you'll often have to bring your hoop to a window, or other light source, in order to see clearly through your fabric - today happened to be an exceptionally bright day, and so I was able to see my design straight through the fabric while sitting at my desk!
Place your pattern underneath your fabric and hold it in place with your hand or a piece of tape.
Make sure to hold your pattern steady as you trace your lines. Because I'm using a pencil in this example, I've only traced over lines that I know I'll be covering with my stitches (pencil marks are incredibly hard to remove from fabric).
It's that simple! If you're having issues seeing through your fabric, and your fabric is definitely light enough to see through, that usually means one of two things:
Your light source isn't bright enough! Try moving to a window, waiting for a sunnier day, or bringing your hoop to another source of light (such as a lightbulb).
The lines on your pattern aren't thick and/or dark enough. You can fix this by drawing over your pattern with a thick marker. If the lines in your pattern are delicate on purpose (for example, if you're working with an intricate line drawing pattern) and you can't darken the lines without losing detail, that could mean that another transfer method might be a better option for you.
I hope this was helpful! Happy stitching!