אל תשמרי קבצים מיותרים על המחשב, כי אחר כך קשה למצוא מה חשוב.

Because Hebrew usually forms a negative command with אל + a future-tense form, not with the regular imperative.

So:

• שמרי! = Save! / Keep! (positive command, feminine singular)
• אל תשמרי! = Don’t save! / Don’t keep! (negative command, feminine singular)

Even though תשמרי looks like a future form, after אל it functions as don’t do X.

It is addressed to one female. The form תשמרי is second person feminine singular.

Other versions would be:

• אל תשמור = to one male
• אל תשמרו = to more than one person
• אל תשמורנה = to a group of females only, very formal/literary

So this sentence is specifically talking to you if you are female.

It comes from the verb לשמור.

The basic meaning of לשמור is to keep, to guard, or to preserve, but in modern Hebrew it is also very commonly used for to save a file or document.

So in a computer context:

• לשמור קובץ = to save a file

This is very natural Hebrew, even though the same verb can also mean things like to guard or to keep in other contexts.

In Hebrew, adjectives usually come after the noun they describe.

So:

• קבצים = files
• מיותרים = unnecessary / redundant

Together:

• קבצים מיותרים = unnecessary files

This is the normal Hebrew word order for noun + adjective.

Because it has to agree with קבצים in gender and number.

• קובץ = file (masculine singular)
• קבצים = files (masculine plural)

So the adjective also has to be masculine plural:

• מיותר = unnecessary (masculine singular)
• מיותרים = unnecessary (masculine plural)

If the noun were feminine plural, the adjective would change too.

Here מיותרים means something like:

• unnecessary
• redundant
• not needed
• extra in a useless way

So it is not just extra in a neutral sense. It usually suggests that the files are there without a good reason and only make things harder.

על המחשב is very natural when talking about files being saved on a computer, similar to English on the computer.

Hebrew often uses על with devices and digital platforms in this kind of way:

• על המחשב = on the computer
• על הטלפון = on the phone

You may also hear במחשב, which can sound more like in the computer or inside the computer/system. In many everyday situations, both are possible, but על המחשב is very idiomatic here.

כי means because, and אחר כך means after that, later, or afterwards.

So:

• כי אחר כך = because afterwards / because later

The adverb אחר כך comes early in the clause to set the time frame: later on, it becomes hard...

Hebrew word order is somewhat flexible, so you could also hear similar variations, but this version sounds very natural.

This is a very common Hebrew structure:

• קשה + infinitive = it is hard to...
• קל + infinitive = it is easy to...
• אפשר + infinitive = it is possible to...

So:

• קשה למצוא = it’s hard to find

Hebrew often does not need an explicit word for it in this kind of sentence. English says it is hard to find, but Hebrew simply says קשה למצוא.

Here מה חשוב means what is important.

So:

• למצוא מה חשוב = to find what is important

This is a compact and natural way to say it. Hebrew often allows this shorter structure when the meaning is clear.

A longer version such as למצוא את מה שחשוב is also possible, and it can sound a bit more explicit. But the shorter למצוא מה חשוב is perfectly normal in everyday Hebrew.

You would change the verb form:

• To one woman: אל תשמרי קבצים מיותרים על המחשב...
• To one man: אל תשמור קבצים מיותרים על המחשב...
• To several people: אל תשמרו קבצים מיותרים על המחשב...

The rest of the sentence stays the same. The main change is in the command form of the verb.