How to learn English words from context instead of flashcards
A word learned inside a sentence you understood stays; a word learned on a card fades. Read at a level where most words are known, let the translation confirm the unknown ones, and let repetition across the book do the memorising.
What a card leaves out
A flashcard gives you a word and a meaning. It leaves out everything that makes the word usable: which words it goes with, what register it belongs to, whether it is said or only written, what it feels like in a sentence. That is why people with two thousand cards still cannot read a page, and why people who have read ten novels know words they never studied.
Vocabulary research has a rough figure for how many times a word must be met in reading before it is known: somewhere between eight and twelve, spread over time and over different sentences. A novel does this for its own vocabulary automatically, because a story repeats its things, its places and its actions.
Reading at the right density
Context teaches only when there is enough of it. If one word in five is unknown, the sentence has no context to give. If one in twenty is unknown, the sentence itself tells you most of the meaning and the translation confirms it. That is the density to aim for, and it is what the level shelves approximate: pick the level where you understand the page and look things up in the gaps.
The routine
Read the sentence. If a word stops you, glance at the translation under the sentence, see how the word was rendered, and read the English again. Do not write anything down yet. When the same word stops you a second or third time in the same book, save it, because now you have met it in several contexts and it is worth keeping.
On Booklern a saved word keeps the sentence it came from. Later, the practice mode writes a short story that uses your saved words in a new context, so you meet them again the way you met them the first time, inside a text, and not as a list.
Where cards still help
Cards are good for two narrow jobs: the first five hundred words of a language, where there is no context yet, and a fixed list you must know for an exam by a date. Even then, a card that carries the sentence you found the word in beats a card with the word alone. For everything else, read.
What to read for vocabulary
Long novels build vocabulary better than short story collections, because a novel repeats its own words for three hundred pages. Detective novels are especially good: a small cast, a small set of places, and the same actions described again and again. A collection of unrelated short stories gives you variety but less repetition, which is better for reading stamina than for words.