'suy' doesn't sound like anything i can recognize. you probably mean 'suyo/suya' 'su', is roughly equivalent to 'his/her'. it doesn't make gender distinction, and is used as a possesive word. for instance: su reloj (his/her watch) ella siempre usa su carisma (she always uses her charms) esa es su taza (that is his/her cup) sus notas siempre son las mejores (his/her scores are always the best) on the other hand, 'suyo/suya' does have gender distinction, and is mostly used to answer a question about who's the owner of something, or comparison. keep in mind this is a form is only used for third persons, not for 'i' or 'you'. examples: 'de quien son estos pantalones?' (whose pants are these? . lit. from who are these pants) 'son suyos' (they are his' . provided the listener knows who the talker is referring to) 'me gusta el arroz de la tia Maria' (i like aunt Maria's rice) 'yo prefiero el de mi madre, es mejor el suyo' ( i preffer my mom's. hers is better) keep in mind the gender used (suyo/suya) depends on the gender of the OBJECT being talked about, not of the subject in the sentence. if you want to talk about second person 'yours', then you must use 'tuyo/tuya'.: 'mi lapiz no funciona, me puedes prestar el tuyo, por favor?' (my pen doesn't work, can you please lend me yours?) 'ese dibujo es tuyo?' (that drawing is yours?) keep in mind this is an 'informal' construction. if you want to make it formal, you can use then use 'suyo/suya', but this is out of the scope of this question! if you need anything else, please send me a message hoping this helps!

"su", "suyo (suya)" son posesivos. Se indican para indicar cuango algo pertenece a alguien: "Esto es "su..." ("esto le pertenece a el"). "esto es suyo o suya" ("esto le pertenece a el o a ella")