Do you mean the spice mix consisting of chile pepper, salt and dehydrated lime? The 'classic' use is on fruit and vegetables. One version of 'pico de gallo' consists of sticks of jicama, cucumber, and tropical fruits seasoned with this mix. Or you can use you own mix of ground chile (guajillo works well), salt, and fresh lime juice. Cilantro is a nice addition.
Pati's version using Tajin
street style vegetables
corn on the cob
It’s uses are varied, many people just use it as a seasoning salt on whatever they are eating, it’s popular to season cucumbers and other fruits with it. There is also a beer cocktail that uses it called mich....... mu memory is fading. Fresh cooked tortilla chips sprinkled with it is also a tasty snack.