comprender vs entender
Both mean 'to understand'. Entender is the everyday verb. Comprender suggests deeper or empathetic understanding — and also means 'to include'.
entender
To understand — language, instructions, how something works.
No entiendo nada.
I don't understand anything.
Stem change e→ie: entiendo.
¿Me entiendes?
Do you understand me?
Checking that you're clear.
Entiende de coches.
He knows about cars.
Entender de = to be knowledgeable about.
comprender
To understand fully, to empathise — or to comprise.
Te comprendo perfectamente.
I understand you completely.
Empathy. 'Te entiendo' can sound more practical.
No comprendo por qué lo hizo.
I don't understand why he did it.
Motives and feelings.
El precio comprende el desayuno.
The price includes breakfast.
Comprender also means to include, to consist of.
Tricky bit
'Comprar' (buy) and 'comprender' (understand) differ by two letters but are not related. 'Entender' is also used for opinions: 'a mi entender' = in my understanding.