daha, en, and kadar
Turkish has no morphological comparative or superlative — no '-er' or '-est'. Instead it uses three words. daha + adjective = 'more X': daha güzel = 'more beautiful'. en + adjective = 'most X': en güzel = 'most beautiful / the most beautiful'. To say 'as X as Y', use kadar ('as much as'): senin kadar = 'as much as you', bir tilki kadar kurnaz = 'as cunning as a fox'. The thing being compared takes the ablative -den/-dan ('than'): benden uzun = 'taller than me'.
More: daha + adjective
Just put daha before any adjective: daha iyi ('better'), daha kötü ('worse'), daha hızlı ('faster'), daha yavaş ('slower'). To name what you're comparing to, mark it with the ablative -den/-dan (it means 'from', and Turkish reasons 'taller from me' = 'taller than me'). Ali Mehmet'ten daha uzun. = 'Ali is taller than Mehmet.' The daha can be dropped when the -den is present, especially in speech: Ali Mehmet'ten uzun. still means 'Ali is taller than Mehmet'.
Most: en + adjective
en marks the superlative: en iyi ('best'), en güzel ('most beautiful / the prettiest'), en büyük ('biggest / largest'). The superlative is often followed by a noun in a compound: en iyi arkadaşım ('my best friend'), en sevdiğim film ('my favorite film' — lit. 'most-I-love-it film'), dünyanın en yüksek dağı ('the world's highest mountain'). With the genitive on what you're picking out of, en lives between the genitive phrase and the head: sınıfın en uzun öğrencisi = 'the tallest student in the class'.
As X as: kadar
kadar means 'as much as / to the extent of'. The thing compared sits in the bare nominative or genitive form before kadar. Senin kadar çalışkan biri yok. = 'There's nobody as hard-working as you.' Bir aslan kadar güçlü. = 'Strong as a lion.' Pronouns take the genitive: benim kadar ('as much as I'), senin kadar ('as much as you'), onun kadar ('as much as he/she'). kadar also means 'until' with time, but for comparison the structure is X kadar + adjective.
Less: daha az
There's no special 'less' word — combine daha ('more') + az ('few/little'). Bu kitap daha az ilginç. = 'This book is less interesting.' Or invert with daha + opposite: daha kolay ('easier') instead of 'less hard'. For 'the least', use en az: en az ilginç film = 'the least interesting film'. Don't try to translate 'less' literally — Turkish prefers 'more of the opposite' or daha az.
Equal-and-not patterns
aynı = 'the same'. Bu iki kitap aynı. ('These two books are the same.') gibi = 'like'. Bir melek gibi. ('Like an angel.') Negate with kadar değil: O kadar zor değil. ('It's not that hard / not as hard as that.') A frequent stock phrase is bir o kadar da = 'and equally / just as much': Çalışkan ama bir o kadar da yorgun. = 'Hard-working, but equally tired.'
