Learn Hardcore Turkish: Sayfanın en altına kaydırıp dosya eklemeyi unutmayın. - Scroll to the very bottom and do not forget to attach the file.

Because Turkish expresses "X of Y" with a possessive construction: the possessor takes genitive (sayfa-nın) and the possessed noun takes a 3rd-person possessive suffix (alt-ı = its bottom). Together: sayfanın altı = the bottom of the page.

What does "en" add here?

en is a superlative/intensifier. alt = bottom; en alt = the lowest/the very bottom. Without en, sayfanın altına is still "to the bottom (of the page)," but en emphasizes going all the way down.

Why is it "altına" and not just "altı"?

The dative -e/-a (here -na due to a buffer n) marks motion “to/toward” a goal. altı = its bottom; altına = to its bottom. You need the dative because the verb implies movement to a location.

Do I need to say "aşağı" (down) here? Could I say "aşağı kaydırıp"?

aşağı kaydırın = scroll down (direction, no specific endpoint).
sayfanın en altına kaydırın = scroll to the very bottom (clear endpoint). Using both together (aşağı… en altına) is redundant. In your sentence, en altına already implies going all the way down, so aşağı isn’t needed.

What exactly does "kaydırıp" mean, and why not "kaydırın"?

kaydırıp is the converb form: kaydır-ıp (“scroll and [then] …”). The suffix -ıp/-ip/-up/-üp links actions in sequence. Only the final verb carries the imperative: unutmayın (don’t forget). If you say kaydırın ve …, you’re putting the imperative on both actions explicitly; with -ıp, it’s more compact and typical in instructions.

Could I use "kaydırarak" or "kaydırdıktan sonra" instead of "kaydırıp"?

kaydırarak = by/while scrolling (means or manner). Here it could sound like “attach the file by scrolling,” which is odd.
kaydırdıktan sonra = after scrolling (clear “after” relationship).
kaydırıp = sequential “scroll, and then…,” which is the most natural here.

What register/politeness does "unutmayın" have? Why not "unutma"?

unutmayın is the negative imperative for you (plural/formal)—used in instructions, signs, UI text, etc. unutma is the informal singular “don’t forget” (to a friend, a child). A very formal alternative is unutmayınız.

How is "unutmayın" formed?

unut-ma-yın

unut- = forget
-ma = negative
-yın = 2nd person plural/formal ending (the y is a buffer after a vowel) Vowel harmony gives -mayın here (vs. -meyin with front vowels).

Why is it "dosya eklemeyi" and not "dosya eklemek"?

Turkish often turns verbs into noun-like objects with -mA. With certain verbs (e.g., unutmak, sevmek, beklemek for actions), that verbal noun normally takes accusative -I:

dosya ekle-me-yi = the act of attaching a file (as an object)
Using bare eklemek here is ungrammatical; unutmak selects the -mA + -(y)I form.

What is the -y- in "eklemeyi"?

It’s a buffer consonant inserted between two vowels: ekleme (verbal noun) + -i (accusative) → ekleme-yi = eklemeyi. Without the y, you’d have a vowel clash.

Why is it "dosya eklemeyi" and not "dosyayı eklemeyi"? Does that change the meaning?

dosya eklemeyi = don’t forget attaching a file / attaching files (indefinite/generic).
dosyayı eklemeyi = don’t forget attaching the file (a specific, known file). In general instructions, the indefinite dosya is common; if a specific file is in question, use dosyayı.

Could I just say "eklemeyi unutmayın" without "dosya"?

Grammatically yes—if the thing to be added is obvious from context (e.g., “the attachment we mentioned”). It’s less clear in isolation. You can also specify with a pronoun: onu eklemeyi unutmayın (don’t forget to add it).

Does "eklemek" here mean “add” or “attach”? What about "yüklemek"?

eklemek means “to add,” and in UI/email contexts it commonly means “to attach” (a file to a form/message). yüklemek means “to upload.” So:

dosya eklemek = attach/add a file
dosya yüklemek = upload a file Choose based on what the interface is actually doing.