Learn Hardcore Spanish (Latin America): Todavía no entiendo esta lección.

Todavía means “still” or “yet” here. It emphasizes that up to now you have not understood the lesson but you expect to understand it later. Without todavía, No entiendo esta lección simply states “I don’t understand this lesson” with no implication about timing.

Can I use aún instead of todavía? Are they interchangeable?

Yes, aún (with an accent) is largely interchangeable with todavía when meaning “yet” or “still.”

Aún no entiendo esta lección.
Todavía no entiendo esta lección.
Both are correct. Some speakers prefer todavía in speech; aún is shorter and slightly more formal.

Why is no placed before entiendo?

In Spanish, negation is formed by placing no directly before the verb. So no entiendo literally means “I do not understand.” You cannot omit no, or the sentence becomes affirmative.

Could I say No entiendo todavía esta lección instead? Does it change the meaning?

Yes, you can swap the order:

No entiendo todavía esta lección.
The meaning stays the same. Placing todavía after the verb is perfectly natural, though starting with todavía puts a bit more emphasis on “still.”

Why is esta written without an accent in esta lección?

Here esta is a demonstrative adjective meaning “this,” modifying lección. According to modern RAE rules, demonstrative adjectives do not carry an accent:

esta lección (“this lesson”)
The accented form ésta used to mark a pronoun (replacing a noun), but accents on demonstratives are generally optional or discouraged now.

Why not just say la lección instead of esta lección?

You can say Todavía no entiendo la lección and it’s correct. Using esta (“this”) is more specific: you’re referring to a particular lesson (perhaps the current one). La lección is more general (“the lesson”), which could be fine if context is clear.

Could I say Todavía no comprendo esta lección? What’s the difference between entender and comprender?

Yes, comprender and entender both mean “to understand.” There is little to no difference in everyday use. Some subtle views:

Entender can be more about grasping facts or mechanics.
Comprender can hint at deeper or emotional understanding.
In practice, they’re interchangeable here.

What about using aprender? Could I say Todavía no aprendo esta lección?

No, aprender means “to learn,” not “to understand.” Saying Todavía no aprendo esta lección would suggest you have not learned the lesson yet (perhaps memorized it), but it doesn’t convey comprehension.

What tense is entiendo, and could I use another tense to say the same thing?

Entiendo is the first-person singular present tense of entender (“I understand”). To express a similar idea, you might use:

Present perfect: Todavía no he entendido esta lección (“I haven’t understood this lesson yet”).
Preterite (less common for “yet”): Todavía no entendí esta lección (implies you didn’t understand it at a specific past moment).
But the simple present no entiendo is the most direct for “I still don’t understand.”