kono rokkaa wo akemasu.

この is a determiner, so it must come directly before a noun: この ロッカー = this locker.

これ is a standalone pronoun, meaning this one. It cannot directly modify a noun.

• この ロッカー = this locker
• これ = this one

So if you want to say this locker, この is the correct choice.

を marks the direct object of the verb. It shows what is being opened.

In この ロッカー を 開けます, the thing being opened is この ロッカー.

So the structure is:

• この ロッカー = this locker
• を = object marker
• 開けます = open

A natural way to think of it is: [this locker] + [object marker] + [open].

In modern Japanese, the particle を is usually pronounced o, not a strong wo.

So this sentence is pronounced roughly like:

kono rokkā o akemasu

You may still see it romanized as wo in some learning materials because historically that was its sound and it helps distinguish it from お, but in normal speech it is basically just o.

This is because 開ける means to open something and is a transitive verb.

• 開ける → 開けます = to open something
• 開く → 開きます = something opens / to open intransitively in many contexts

In this sentence, there is a direct object marked by を: this locker. That means the speaker is actively opening the locker, so 開けます is the right verb form.

A useful contrast:

• ドアを開けます。 = I open the door.
• ドアが開きます。 = The door opens / is opening.

The dictionary form is 開ける.

開けます is the polite -ます form. Many beginner sentences use -ます because it is standard polite Japanese.

So:

• dictionary form: 開ける
• polite form: 開けます

It can mean either, depending on context.

Japanese -ます forms do not always separate present and future the way English does. So 開けます can mean:

• I open this locker
• I will open this locker

The surrounding situation tells you which is meant.

Yes. Japanese often omits the subject when it is clear from context.

So この ロッカー を 開けます does not explicitly say who opens the locker. Depending on context, it could mean:

• I open this locker
• We open this locker
• He/She opens this locker

In many real conversations, Japanese leaves out information that both speaker and listener already understand.

Japanese normally does not use spaces between words in standard writing.

So the sentence would usually be written as:

このロッカーを開けます。

Spaces are often added in beginner materials to make it easier to see the parts of the sentence.

ロッカー is a loanword, borrowed from English locker, so it is written in katakana.

Katakana is commonly used for:

• foreign loanwords
• foreign names
• sound effects
• emphasis in some cases

So ロッカー being in katakana is completely normal.

Normally, no. この needs a noun after it.

• この ロッカー = this locker
• この by itself is incomplete

If you want to say this one, use これ instead.

So:

• このロッカーを開けます。 = I open this locker.
• これを開けます。 = I open this one.

The basic order is:

noun + particle + verb

More specifically here:

この ロッカー + を + 開けます

Japanese verbs usually come at the end of the sentence, so unlike English, the action word often appears last.

English: I open this locker.

Japanese: This locker + object marker + open.

Yes. The plain form would be:

このロッカーを開ける。

This is less polite than 開けます.

So the difference is mainly politeness level:

• 開けます = polite
• 開ける = plain / casual

Both can mean basically the same thing, but they are used in different social situations.