tratar vs tratarse
Tratar de is to try. Tratar a is to treat someone. Tratarse de is 'it's about'. Three prepositions, three meanings.
tratar
To try (tratar de), to treat or behave towards (tratar a), to deal with (tratar sobre).
Trato de llegar a tiempo.
I try to arrive on time.
Tratar de + infinitive. Same as intentar.
Me trata muy bien.
He treats me very well.
Behaviour towards someone. Tratar a + person.
El libro trata sobre la guerra.
The book deals with war.
Subject matter. Tratar de/sobre.
tratarse de
To be about, to concern — an impersonal use, always with 'se' and 'de'.
¿De qué se trata?
What's it about?
The standard question for a plot or a meeting.
Se trata de un malentendido.
It's a misunderstanding.
Se trata de + noun = it's a matter of.
Se trata de ser honesto.
It's all about being honest.
Se trata de + infinitive = the point is to.
Tricky bit
'Tratar' with a subject like 'la película' = the film is about. But 'se trata de' has no real subject. 'La película se trata de amor' is a heard error — say 'la película trata de amor'.