Hi, i want's to know what file I have to change for a different layout of categories on main page

This is an example:

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Canon <- main cat.

Serie bjc <- subcat 1st lelvel

BJC 2000 BJC 4000 <- subcat 2nd lelvel
BJC 2100 BJC 4100

Serie i <- subcat 1st lelvel

i250 i550 <- subcat 2nd lelvel
i320 i560

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Thanks a lot and bye