Tu vs Tu'
Is tu' (that is with the accent) used only when it is the subject? Or is there another rule that determines when you use the accented u and when not?
Accented (PRONOMBRE PERSONAL, doing or receiving an action): Tú escribes (you write) / Yo soy como tú (I am like you) || Not Accented (ADJETIVO POSESIVO, always before a name): tu lápiz (your pencil) / tu duda (your doubt)
Only when it is used as a pronoun, yes. Such as its use in "You know?!" : "¡Tú sabes! Just as the way it is used in Selena's song "Como la flor".. she says "Me diste tú"
Good answers. I also wish to add that using tú as a subject with the verb us usually unnecessary as the verb tells us which person is doing the action e.g. hablas clearly means tú hablas but it can be used for emphasis. Also to write a vowel with an accent, press Alt Gr (I have an English keyboard) and the vowel or use a program such as "acento program" which can be used to write accents.