To Treat
As in a person or medically
Jimmy treats Kimmy well.
The doctor treated the illness with medicine.
Tratar (alone— no “de” following and not reflexive)
Jimmy trata bien a Kimmy.
El médico trató la enfermedad con medicina.
To Try or To Attempt
Jimmy tried to buy chicken.
Tratar de + infinitive
Jimmy trató de comprar pollo.
Note: There are other more common ways to say this using “Intentar “
Jimmy intentó comprar pollo.
When “trying” a sample always use “Probar”.
To be about something
To have to do with something.
This book is about Jack Nicholson.
Tratarse de
Este libro se trata de Jack Nicholson.
More common to use “Sobre” instead of “Tratarse de”.