Eva, a burrito is a large flour tortilla, stuffed with a filling, ends tucked in, and rolled up
like a great big blintz. It's usally a complete meal, stuffed, for instance, with stewed meat, rice and beans. It's lunch cart fare and ususally eaten by hand, but restaurants often douse them with sauce and cheese and run them under the broiler.
An enchilada is a smaller tortilla, either corn or flour, that's usually fried first, dipped in a sauce, rolled around a simple filling like a crepe, open at the ends, and baked with cheese. The filling would be meat or cheese, It's eaten with a knife and fork, with rice, beans etc. on the side
Fajitas are marinated meats that are sauteed quickly with onions and peppers, and served right away with a selection of accompaniments such as salsas, guacamole, lime wedges and sour cream, along with warm tortillas. Restaurants make a big deal out of rushing the hot skillets to the table. The diners assemble their own tacos by filling the tortillas with whatever combination they like, folding, and eating out by hand.