Kazan is a big city about 200 km away from Cheboksary. You can come there with the direct flight from Bangkok, Munich, Prague, Istanbul, Antalya and Frankfurt. But first you need to check this, because the schedule changes often.
From Kazan you will need to take a bus to Cheboksary and you will be here in about 3 hours.
Step#1 Go out of the Airport building and take a bus № 97. You need to come to Academik Sakharov str. (улица Академика Сахаров) bus stop.
Step#2 There you should take a trolleybus №20 and go to the Bus station. There buy a ticket to Cheboksary. It costs 320 roubles.