Here are the things you will need. It's really, REALLY important to cover your work area, as this is a pretty messy project. That's what the trash bag is for.

Technically you should probably wash whatever fabric you are using before you get started. (I am impatient and bypassed that step with no ill effects.) Dampen the front of your shirt with the spray bottle then flip it over and give the back a good spray too. A slightly wet shirt will soak up dye a lot quicker/easier than a dry one.

Now for the folding process.

If you ever made a paper fan as a kid, then you already know how to fold the shirt. If you never made a paper fan as a kid, then I can't help you. Just kidding. Do an image search for 'accordion fold' and you'll get the idea.

Finished folds.

Use the binder clips to hold your folds in place while wrapping the bands.

The bands need to be nice and tight to keep the dye from sinking into the parts that will remain lighter or white. My stripes turned out a slightly lighter blue than the rest of the shirt; if you want whiter stripes, use wider rubber bands. Place a band wherever you want a garment-colored stripe, removing the binder clips as you go.

I stopped before I got to the top of my shirt because I wanted to leave that part white.

I still put a few rubber bands on the top part just to keep the top of the shirt from flopping around too much.

I also wrapped that portion in plastic wrap. Some dye will still bleed into that area, but the plastic wrap will keep any dye splatters from getting on the part that is to remain white. Secure the plastic wrap to the shirt with a few more rubber bands.

Mix dye according to the directions it came with. Mine didn't come with instructions for dying with a bottle, so I put half the dye packet and about a teaspoon of salt in the condiment bottle, filled it with hot water and shook it to mix everything together (be sure you put a finger over the bottle opening). This was easily enough dye for two shirts.

*Be extremely careful with the dye packet! The powdered dye will stain anything it comes in contact with! Skin, countertops, hair; this stuff does not discriminate!!*

Squirt the dye directly onto the tee, making sure to flip the shirt over from time to time to really work the dye into all areas of the fabric.

Then wrap the entire shirt in plastic wrap and let sit for six to eight hours (less if you want a more muted hue of whatever color you are using). I left mine over night and ended up with a nicely saturated navy. I don't know why I didn't take a picture of this step, but all that really matters is that none of the die leaks out.

Put on gloves and rinse the shirt. If you left a white bit at the top, rinse from the top down. I left the bands on until the water ran clear, then removed them and continued rinsing. This was the result.

All that's left is to wash and dry the shirt according to the directions on the dye (I washed in warm water and hung it to dry). This is the final result. Pretty sweet for a $2 tee.