In many languages, adjective order is fixed and simple: the noun comes first, then the adjective follows it, with the adjective agreeing only in gender, as in "pants blue" said the other way around. German flips this completely: the adjective always comes directly before the noun, as in ein blauer Pullover (a blue sweater), literally "a blue sweater" with blue in front. That word order is the first habit to build.
But harder than the word order is the fact that a German adjective placed before a noun takes a changing ending, decided by three factors together: the noun's gender (masculine, feminine, or neuter), its grammatical case (nominative or accusative here), and the type of article in front of it (ein, eine, or none at all). This is a genuinely new concept for many learners, since in everyday speech an adjective often stays the same regardless of its grammatical role in the sentence.
This lesson focuses on adjectives after ein or eine in the accusative case — that is, when the adjective and noun together are the direct object of a verb like kaufen (to buy) or möchten (would like). With masculine nouns, add -en, as in einen roten Pullover; with feminine nouns, add -e, as in eine blaue Hose; with neuter nouns, add -es, as in ein weißes Hemd; and with plurals (no article), add -e, as in rote Schuhe. These endings are not random — they follow a pattern that reappears elsewhere in German, and you'll recognize it more and more as you progress.
The second point in this lesson is the demonstrative dieser/diese/dieses (this), extremely useful when shopping to point at a specific item in front of you. The good news is that it behaves exactly like der/die/das that you already know: dieser for masculine, diese for feminine and plural, dieses for neuter, and in the accusative, masculine dieser becomes diesen — just as der becomes den.
Finally, the word zu here means "too" (excessively), not the more familiar "to": Das ist zu teuer means "this is too expensive." It's extremely handy for complaining about price or size while shopping.
A very common mistake among beginners is forgetting to change the adjective ending, or always defaulting to -e because it feels easiest, producing einen blaue Hose instead of eine blaue Hose — the mind isn't yet used to one adjective wearing different endings depending on the noun it describes. Practical tip: instead of memorizing the rule in the abstract, memorize whole ready-made phrases like einen roten Pullover and eine blaue Hose, and the pattern will start to feel natural over time.