אל תיגעי בכתם הזה; אני אנסה לנקות אותו אחר כך.

Because Hebrew marks gender in the second person.

• אל תיגעי = don’t touch (said to one female)
• אל תיגע = don’t touch (said to one male)
• אל תיגעו = don’t touch (said to more than one person)

English doesn’t do this, so it often feels unusual at first.

In Modern Hebrew, negative commands are usually formed with אל + a future-tense form.

So:

• אל תיגעי = don’t touch (to one female)

This is the normal way to say a negative command.
A positive command would use an imperative form instead, such as געי! = touch! (to one female).

Because the verb לגעת (to touch) normally takes the preposition ב־ in Hebrew.

So Hebrew says, literally:

• לגעת בכתם = to touch a/the stain

Even though English says touch the stain with no preposition, Hebrew uses ב־ here.
So after תיגעי, you expect בכתם, not את הכתם.

It has merged into the preposition.

In Hebrew, the prepositions ב־, ל־, and כ־ often combine with the definite article ה־:

• ב + הכתם → בכתם

So בכתם הזה means in/on the stain הזה, which in natural English is this stain.

This is very common in Hebrew.

Because in Hebrew, demonstratives like this usually come after the noun:

• הכתם הזה = this stain
• הספר הזה = this book
• הילדה הזאת = this girl

So Hebrew uses noun + this, not this + noun.

In your sentence, because of the preposition, you get בכתם הזה.

From the words that agree with it:

• הזה is masculine singular
• אותו is also masculine singular

So כתם is a masculine noun.

If it were feminine, you would expect forms like:

• הזאת
• אותה

It can mean him or it, depending on context.

Hebrew uses the same direct-object pronouns for people and things.
Here, אותו refers to כתם, which is a masculine singular noun, so it means it:

• לנקות אותו = to clean it

If the noun were feminine, Hebrew would use אותה.

Because once the stain has already been mentioned, Hebrew—like English—often switches to a pronoun.

So both are possible:

• אני אנסה לנקות אותו אחר כך = I’ll try to clean it later
• אני אנסה לנקות את הכתם אחר כך = I’ll try to clean the stain later

Using אותו sounds natural because the referent is already clear.

The ל־ here marks the infinitive, like English to.

• לנקות = to clean

So:

• אני אנסה לנקות = I will try to clean / I’ll try to clean

This is a very common pattern:

• אני רוצה לאכול = I want to eat
• היא התחילה ללמוד = She started to study

Literally, it means I will try.

In this sentence, it works naturally as:

• I’ll try

Hebrew often uses the future tense this way to express intention, willingness, or a plan.

אחר כך means afterward, later, or after that.

In this sentence:

• אני אנסה לנקות אותו אחר כך = I’ll try to clean it later

It often appears at the end of the clause, but it can also be moved for emphasis:

• אחר כך אני אנסה לנקות אותו

Only the command part changes.

• To one man: אל תיגע בכתם הזה; אני אנסה לנקות אותו אחר כך.
• To one woman: אל תיגעי בכתם הזה; אני אנסה לנקות אותו אחר כך.
• To several people: אל תיגעו בכתם הזה; אני אנסה לנקות אותו אחר כך.

The second clause stays the same because אני אנסה still means I will try.

Roughly, tig-'i.

There is a slight break before the final -i in careful pronunciation because of the letter ע. In everyday Modern Hebrew, many speakers pronounce that ע very weakly, so it may sound closer to tigi.