'then' is related to time and sequencies. For example "Read this book then read that book". 'than' is related to comparison. For example "5 is greater than 3" Probably I missed some cases. I guess that somebody may provide more information.

They are completely different words. 'Then' means next, or at that time. We use 'now' for the present time, and 'then' for other times - either past or future. For example, 'I had a shower, and then I got dressed' or 'I didn't go to Australia when I was a student because I didn't have enough money then'. 'Then' can also have the meaning of 'so'. 'I'm hungry.' 'Then eat something!' 'Than' only has one use - it's the word we use when we're comparing two things, for example, 'My brother is older than me.' I hope that helps.

Than....is used to compare two things or actions... This garden is more beautiful than that garden.. Then is used to show elapse of time..sequencing events...First, I went to the store then, I went to the bank.