What is the difference between tratar and probar?
I'm never sure when to use tratar or probar. I think that they both mean 'to try' but are their meanings different? Or can I use them interchangeably?

Question

Answer

Probar - (to test) – Quiero una clase de prueba con esta escuela.  
Probar - (to taste) – El no probó los vegetales por que sabía que no le iban a gustar.
Probarse - (to try on) – Me gustaría probarme esta camisa.
Tratar de - (to attempt) – Estoy tratando de aprender Español.  ***Note that without the “de” the translation will then be, “to treat” or “to deal with”, so be careful!

Answer

Tratar y probar have different meanings. Regarding the one you are asking as 'to try, you will need prepositions most of the times:
Tratar de:  Trato de aprender portugues  ( it's implied the achievement of the action); 
Probar a: Pruebo a aprender portugues ( I can try/try out  but it does not have implied the achievement)

Hope it makes sense :)

Answer

"tratar" es como "try", intentar algo. También se usa cuando se acuerda algo entre dos personas (se cierra un trato)
"probar" es hacer una prueba, como un "test", por ejemplo probar que algo funcione correctamente

Answer

"tratar de + infinitive" = to try 
"Quiero tratar de ser mejor." (I wanna try to be a better person.)

"probar a + infinitive" = to try, but implies a previous choice or decision
"No se si servirá de algo, pero voy a probar a ser mejor." (I don't know if it's worth but I will try to be a better person.)

Anyway both "tratar" and "probar" have other meanings:
"tratar" = to address, to treat...
"probar" = to taste, to check, to demostrate...