Just drag the clothes onto Dobi to dress him up!
To capture your finished image:
Press the "Print Screen" key on your keyboard (usually on the top right of your keyboard, near the Scroll Lock key), paste the screen image into Paint or another image editing program and crop it.
I'm sure Dobi would love to see what you've dressed him in, so why not send them in? (See above for information on how to capture your pictures).