"Debo" , comes from "deber" and well, "deber" can mean different things.
One , of course, means "I have to", "I must" or "I should" as in "Debes ir a la escuela" (You must go to school/You have to...), "Yo debo hacer mi tarea" (I have to make my homework).
The 2nd meaning is similar to "owing" something, such as money . For example, "Te debo 5 dolares" (I owe you 5 dollars). "Yo le debía dinero al banco" (I owed/Use to owe money to the bank)
The 3rd I can think of is "duty" as in "Es el deber de un soldado servir a su patria" (It is a soldier's duty to serve his homeland). In this case 'deber' never changes , it can't be conjugated, It is more of a adjective.
There is a another way people use 'deber' it is a plural form (I guess) similar to the last meaning (duty) and that is "deberes". It is used a lot when reffering to house chores ("Los deberes del hogar o de la casa") It is something like a responsibillity or assigment.
And now comes TACOS. In Mexico, probably 98% of time, we are talking about...well...THE BEST FOOD IN THE WORLD, a tortilla, rolled or folded around ANYTHING you want, yes! literally you can make tacos out of anything!!!! Meat, pork, chicken, eggs, fish, vegetables,shrimp,lobster insects, potatoes, chorizo, ham, turkey,octopus ,avocado,beans, rice, bacon, roast beef, duck, you can even make a taco inside a quesadilla...well, you get the idea!
But... we also call the billiard or pool stick, "Taco de billar", our soccer/football shoes "tacos de futbol" (similar to the word tacón, which is a high heel) we also use the diminutive of taco (taquito) to describe a soccer pass using the back part of a shoe, or the heel. In Chile and some parts of Colombia, they use Taco as in "traffic jam".
I think I will go get some "Tacos al pastor" (http://en.wikipedia.org/wiki/Al_pastor) right now! I'm starving!
Saludos desde Tijuana, Baja California!