Then is used for time, and than is a comparative word. First mix the ingredients then bake it. I am bigger than you. Some native speakers that can't spell properly sometimes mix them up.

Then - It is used as either an adverb or adjective. Examples/ At a certain time: "Where were you at three o'clock?" "I was at school then." Next in time or order (order of events): "We went to the park, then we went to a restaurant." In addition: "First you need a license, then you can drive." In that case: "If I can't find the classroom, then I can't take the test." Most uses of 'then' have to do with time so keep in mind sentences regarding 'next in time' or 'at the time'. Than - It is used for making comparisons Examples/ "I would rather sleep than read." "I like red more than blue." "Burgers are better than salads."