For my answer I am assuming you want to know about guys referring to potential girlfriends/lovers/dates and not sister's moms, and grandmas.
Anyway it really depends on the context, but generally "pretty", and "cute" means ok looking... like between a 5 to 8 out of 10.
In other words, she isn't ugly, but she isn't gonna turn heads walking down the street. However something about her... her smile, laugh, personality, etc., is cute or pretty and guys get attracted to that once them see it enough.... IE you meet a girl, you never really noticed she was hot, but then after talking to her for 20 minutes, you find you can't stop staring at her dimples when she smiles, or her baby blue eyes, or her laugh makes you smile, etc., MOVING ON
Hot and sexy means this is a girl that a guy wants to have sex with, she has a great body (definition of great varies guy by guy), she is great looking, and basically most guys that see her want to have sex with her. The term sexy comes from the idea that the person looks like someone you would have sex with.
Beautiful and gorgeous are generally terms for a girl who leaves you breathless, looks like an angel, love at first site kind of deal. Supermodels are beautiful, celebrities are gorgeous.
Since your a girl I'll translate to girl language.
Matt Damon would be an example of cute.
Brad Pitt or George Clooney would be hot/sexy.
Some male underwear model with a 6 pack, perfect skin, etc., is beautiful or gorgeous.