Taco is generally in a crisp corn tortilla shell (you know tortilla chips?) Sometimes they are 'soft shell' which is a flour tortilla. They can come as lots of variety. Chicken, beef, shrimp..etc.
Burrito is generally beans (sometimes refried, sometimes just beans..either black or pinto) and whatever the particular restaurant puts in a soft tortilla. Cheese is usually involved...
Taquito is beef (I'm not sure they do other meats) rolled in a tortilla and then fried (someone please correct this one if I'm wrong..my husband loves them but I don't get them often)
Enchelada is sorta open to interpretation depending on where you go. Some places put beans and rice in them. Cheese enchelada is a favorite of a lot of people. Just cheese in a flour tortilla and then smothered with sauce (green chile, red pepper..etc) Lots of times they do meat and cheese in an enchelada..the main point being that this item is smothered in sauce and sometimes cheese.
Don't know on Tostada
Carne Asada is Spanish for Steak
Pico De Gallo is basically onions, tomatoes, lime juice, cilantro, jalapeno...making up a fresh salsa. Yummmmmm