For a noun that ends in a consonant, simply add 'a' For a noun ending in 'й', replace it with 'я' For a noun ending in a soft sign 'ь', replace it with 'я' For plurals, the blanket rule is to add 'ов', UNLESS the noun ends 'ж,ч,ш,щ,ь' in which case you add 'ей', OR 'й, ц' in which case you add 'ев'.