Learn Hardcore Turkish: Lütfen sayfayı en alta kaydırın, onay kutusunu işaretleyin. - Please scroll to the bottom of the page and tick the checkbox.

The vowel is -ı (not -i) due to vowel harmony (last vowel of sayfa is a back vowel).
The buffer letter y appears because the noun ends in a vowel. If the object were indefinite, you’d drop the accusative: Bir sayfa kaydırın = “Scroll a page” (rare, and usually not what you want in UI text).

What does en alta mean, and why is it -a (alta) rather than -ta (altta)?

En alta means “to the very bottom.” The -a/-e ending is the dative case, used for movement toward a goal. -ta/-te (locative) means “at/in/on” a place. So:

en alta = to the bottom (direction)
en altta = at the bottom (location) With a motion verb like kaydırmak (to scroll/slide), you need the directional dative: en alta kaydırın.

What does en add here?

En is a superlative/intensifier meaning “most/very.” With location words it gives the extreme point:

en alt = the very bottom
en üst = the very top
en son = the very end So en alta = “to the very bottom.”

What does the -ın/-yin ending in kaydırın and işaretleyin express? Am I addressing one person or more than one?

-ın/-in is the 2nd person plural or formal singular imperative. It can address:

one person politely/formally (like English “please …”), or
more than one person. So kaydırın/işaretleyin is the standard polite/neutral instruction on interfaces and signage.

Can I say kaydırınız / işaretleyiniz for extra politeness?

Yes. -iniz/-ınız/-unuz/-ünüz is a more formal, sometimes “sign-like” imperative: Lütfen bekleyiniz is common on public notices. It can sound stiff in everyday speech; -in/-ın is usually fine in UI text.

Why does işaretleyin have a y in it?

Because the verb stem ends in a vowel. The imperative suffix is -(y)in. If the stem ends with a vowel, insert the buffer y:

işaretle + (y)in → işaretleyin
bekle + (y)in → bekleyin No buffer is needed after a consonant: kaydır + ın → kaydırın.

Why is there an n in kutusunu?

That’s another buffer letter. Onay kutusu is a compound whose second word carries 3rd person possessive -sU (see next question). When you add the accusative -(y)I / -(y)U to a possessed noun, Turkish inserts a buffer n: kutusu + (n)u → kutusunu.

Why does onay kutusu have -su in it?

Onay kutusu is an “indefinite compound noun.” In these, the second element takes 3rd person possessive -sU (with vowel harmony), while the first element has no genitive:

onay kutusu ≈ “approval box” → “checkbox”
şifre yöneticisi = “password manager” When you mark it accusative (definite object), it becomes onay kutusunu.

Could I just say kutuyu instead of onay kutusunu?

Kutuyu is “the box,” which loses the specific term “checkbox.” You want onay kutusunu. Another common UI term is the diminutive onay kutucuğu (“little box”), accusative onay kutucuğunu—also fine.

Why is it kaydırın with ı, but işaretleyin with i?

Vowel harmony. The imperative suffix appears as -ın/-in/-un/-ün depending on the last vowel of the stem:

After back vowels (a, ı, o, u): -ın/-un → kaydırın, tıklayın
After front vowels (e, i, ö, ü): -in/-ün → işaretleyin, görüntüleyin

Could I say sayfanın en altına kaydırın instead of sayfayı en alta kaydırın?

Yes. Sayfanın en altına kaydırın explicitly says “to the very bottom of the page.” In sayfayı en alta kaydırın, the possessor “of the page” is omitted because it’s clear from context (you’re already scrolling the page). Both are natural.

Can I use aşağı or en sona here?

aşağı means “down(ward).” Sayfayı aşağı kaydırın = “Scroll the page down.”
en sona means “to the very end” (often of a list/sequence). In many UI contexts it overlaps with en alta when the list is vertical: En sona kaydırın can work too. If you specifically want “all the way to the bottom,” en alta (or sayfanın en altına) is clearest.

Is the comma necessary between the two imperatives? Could I use ve?

The comma is just separating two sequential commands. You can also use ve:

Lütfen sayfayı en alta kaydırın ve onay kutusunu işaretleyin. Both are fine; using ve sounds slightly more connected.

Where should I put Lütfen? Do I need a comma after it?

Most natural is at the start: Lütfen … Some writers add a comma after it (Lütfen, …), others don’t—both are acceptable. You can put it later (… kaydırın lütfen) for a softer tone, but initial position is standard in instructions.

Is işaretlemek the same as tıklamak or seçmek?

işaretlemek = to mark/tick/check (what you do to a checkbox).
tıklamak = to click (a button/link).
seçmek = to select/choose (common for radio buttons or selecting items). In checkbox instructions, onay kutusunu işaretleyin or onay kutusunu seçin are both seen; tıklayın refers to clicking, not the state change per se.

How would this sound informally to a friend?

Drop the polite plural and use singular imperatives:

Sayfayı en alta kaydır, onay kutusunu işaretle. You can still keep Lütfen for politeness: Lütfen sayfayı en alta kaydır, onay kutusunu işaretle.