What's the difference between fajitas, enchiladas and tacos?
Enchiladas are normally shredded meat and/or cheese rolled in corn tortillas, covered in red (or green) enchilada sauce and cheese, and then baked.

Fajitas are normally strips of meat either grilled or sauteed (often with onions and peppers). They can be used in tacos, burritos, or served on their own or with tortillas on the side (corn or flour depending on preference). 

Tacos can be either hard or soft shelled and are usually meat (shredded, ground, grilled etc) with some sort of cold veggies (like lettuce, raw onions, pico de gallo, etc) and perhaps cheese etc.