Sit on the toilet, bear down (like you're having a bowel movement), then slowly guide the applicator in. When your fingers touch your lips slowly push the end of the applicator with one finger while still bearing down so your vagina stays open. When that one finger on the end of the applicator touches your other two fingers that are your lips slowly guide the applicator out. Then you're done! 

The string should be hanging out of your body. And you shouldn't be able to feel the tampon inside. If you do that means it's in at the wrong angle and will hurt when you sit down. If that's the case get back on the toilet, bear down and tug on the string GENTLY so you can slowly guide the tampon out. Pulling it out too fast can cause pain. When it's out try again. NEVER put in a second tampon when you have one in already.