In the movie Perfume: The Story of a Murderer it's like he liked the first girl's fragrance so much so he just tried to smell her closely, but why does he keep on killing other girls? Was he getting attracted by other girls' fragrance, too? And what did he achieve by killing girls?
The movie uses scent as a symbol of love. The main character was robbed of love at birth when his mother was killed, and therefore spends his entire life searching for love, and hurting other people along the way. Unfortunately, being deprived of his mother's love meant he never learned to love himself, and therefore is incapable of loving anyone else. In the end he finally realizes his tragic condition, leading him to take his own life.
The movie opens with the main character losing his mother immediately after he was born. He then grows up without a scent of his own, but with a relentless nose for other people's scents -- a peculiarity which drives other people away from him. As he ages, his obsession with other people's scents causes him to kill several women in an effort to capture each of their scents as he searches for the perfect scent.
The interpretation is that the main character keeps searching for the perfect scent just like some men keep searching for the perfect woman, or like addicts keep searching for the escape of getting high. Each time the main character is able to capture a woman's scent, he finds himself unsatisfied and kills the woman -- just like real-life "Don Juans" are unable to find long-term happiness in a committed relationship, or like real-life addicts are unable to avoid the inevitability of coming down. Each woman the main character kills represents a sexual conquest that ends in the woman's heartbreak, or a bender that ends in the inevitable painful hangover.
Overall, the main character is driven by his fractured childhood relationship with his mother, which left him with no scent of his own -- just like real-life Don Juans and other addicts are thought to be driven by "mommy issues" that leave them unable to love themselves. The main character's suicide at the end symbolizes the two most common outcomes for the main character's real-life counterparts: either self-destruction or a life-saving relinquishment of their self-destructive ways.
but why does he keep on killing other girls? Was he getting attracted by other girls' fragrance, too?
Short answer: Grenouille is a clear psychopath who only cares about preserving women’s smells in a perfume.
The key scene to understand Grenouille‘s motivation is when he accidentally kills the plum girl. He cares only about her smell, not about the person. He doesn’t even notice that he killed her until he releases her, and even then he is merely surprised, not shocked or griefed. Only when her smell fades, Grenouille becomes upset, because something beautiful to him turned out to be ephemeral. He then becomes obsessed with preserving smell, clearly to apply it to smells such as the plum girl’s.
On his quest for preserving smells, he learns about formal perfume composition (3×4+1 ingredients) and encounters a new smell of his desire (Laure Richis). This slightly modifies his goal to that of creating a perfume of preserved women’s smells with Laure being the centre piece. So, yes, other women’s fragrances are still attractive to him.
And what did he achieve by killing girls?
Short answer: He achieved that he could perform his procedure on them without hassle.
Grenouille’s procedure could technically be performed on a living woman: She would just have to let him smear her with fat and completely shave her. In his first attempt with the prostitute, he probably did not plan to kill her until she became grossed out by the procedure and refused to participate. On the other hand, given that he does not care about the person behind the smell at all, his only reason to keep her alive was to avoid her smell fading, which then turned out not to be necessary. Since finding women who would willingly undergo his procedure (alive) was practically impossible for him, he resorted to just killing them.