Adónde, A dónde, Adonde y A donde
Adónde/A dónde is an interrogative/exclamative adverb that expresses location. It can be written in one word (adónde) or in two (a dónde), doesn't matter which.Abuela, ¿adónde/a dónde va cargando esas bolsas tan pesadas? Déjeme que le ayude, ¡se va a hacer daño!
Grandma, where do you think you are going with those heavy bags? Let me help you, ¡you are going to hurt yourself!
¿Adónde/A dónde fuiste de vacaciones el año pasado?
Where did you go on vacation last year?
Adonde/A donde is a relative adverb that expresses location but it cannot be used in questions. It can be written in one word (adonde) or in two (a donde), doesn't matter which.
Recuérdame siempre, allá adonde/a donde vayas.
Always remember me, wherever you go.
El parque adonde/a donde vamos está cerca de la biblioteca.
The park where we are going is near the library.
Sino y Si no
Sino is a coordinate conjunction that expresses adversity. It can also have the same meaning as "más que" or "otra cosa que".No sólo no me ayudó sino que además miró para otro lado.
Not only didn't he help me, but also looked the other way.
Tu hermano no tuvo la culpa sino tú.
It wasn't your brother's fault but yours.
Cuando llegamos a Alemania, nos dimos cuenta que no teníamos euros sino dólares.
When we arrived in Germany, we realized that we had dollars instead of euros.
Sino can also be a noun that it's used as a synonym for "destino" (destiny).
No sé lo que me deparará mi sino (destino).
I don't know what my destiny will bring me.
Si no is the combination of the conditional conjunction "si" followed by the negative adverb "no".
Si no vienes a cenar, llámame para avisarme y no prepararte nada.
If you are not coming for dinner, call me in order to not make any food for you.
Haz los deberes si no quieres que me enfade.
Do your homework if you do't want me to get mad.