Meine Schwester speichert das Dokument in der Cloud, damit ich es auch sehen kann.

Because Schwester is a feminine noun in German.

The possessive mein- changes its ending depending on the noun’s gender, number, and case. Here, Schwester is:

• feminine
• singular
• nominative (the subject of the sentence)

So you need meine Schwester.

Compare:

• mein Bruder = my brother
• meine Schwester = my sister
• mein Dokument = my document

Speichert is the 3rd person singular present tense form of the verb speichern, which means to save / store.

The subject is meine Schwester, which is she, so the verb is conjugated like this:

• ich speichere
• du speicherst
• er/sie/es speichert
• wir speichern
• ihr speichert
• sie/Sie speichern

So Meine Schwester speichert ... means My sister saves/stores ...

Das Dokument is the direct object of the verb speichert—it is the thing being saved.

The noun Dokument is neuter, so its basic article is das.

Here it is in the accusative case, because it is the direct object. For a neuter noun, the article is still das in the accusative singular:

• nominative: das Dokument
• accusative: das Dokument

So although the case changes, the article happens to look the same.

Because this sentence describes location, not movement.

The preposition in is a two-way preposition, which means:

• dative for location: where?
• accusative for movement/direction: where to?

Here, the document is being stored in the cloud as a location, so German uses the dative:

• in der Cloud = in the cloud

Compare:

• Das Dokument ist in der Cloud. = The document is in the cloud.
• Sie lädt das Dokument in die Cloud hoch. = She uploads the document into the cloud.

Also, Cloud is treated as a feminine noun here, so:

• nominative: die Cloud
• dative: der Cloud

Damit introduces a purpose clause. It means so that or in order that.

So:

• ..., damit ich es auch sehen kann.
• ..., so that I can also see it.

This tells you the purpose of saving the document in the cloud.

A useful idea:

• weil = because
• damit = so that / in order that

So damit answers the question for what purpose?

Because damit starts a subordinate clause, and in German subordinate clauses the conjugated verb goes to the end.

Main clause:

• Meine Schwester speichert das Dokument in der Cloud

Subordinate clause:

• damit ich es auch sehen kann

If this were a normal main clause, it would be:

• Ich kann es auch sehen.

But after damit, the verb placement changes:

• ..., damit ich es auch sehen kann.

So the key rule is:

• In a main clause, the finite verb is usually in second position.
• In a subordinate clause, the finite verb goes to the end.

Because this clause contains a modal verb: kann.

In German, with a modal verb:

• the main verb stays in the infinitive
• and in a subordinate clause, the modal verb goes all the way to the end

So:

• main clause: Ich kann es sehen.
• subordinate clause: ..., damit ich es sehen kann.

That is why you get sehen kann at the end.

Es refers to das Dokument.

Since Dokument is a neuter noun, the matching pronoun is es:

• das Dokument → es

So instead of repeating das Dokument, German uses the pronoun:

• ..., damit ich es auch sehen kann.
• ..., so that I can also see it.

Here es is in the accusative, but for es, nominative and accusative look the same.

Auch means also or too.

In this sentence, it suggests that I can see the document as well—probably in addition to someone else.

• ..., damit ich es auch sehen kann.
• ..., so that I can also see it.

Its position matters because auch often stands near the part it emphasizes.

Here it naturally emphasizes the idea that I too / I also can see it.

German word placement with auch can be flexible, but learners should notice that it often comes before the element or idea being emphasized.

This is a very common question.

German often uses um ... zu for in order to, but only when the subject of both parts is the same.

Example:

• Ich speichere das Dokument, um es später zu lesen.
• I save the document in order to read it later.

Here, I do both actions.

But in your sentence, the subjects are different:

• Meine Schwester saves the document
• ich see it

Because the subjects are different, German uses damit, not um ... zu.

So:

• Meine Schwester speichert das Dokument in der Cloud, damit ich es auch sehen kann.

That is the correct structure.