يضغط صديقي القاعدة.

يضغط is the imperfect form of the verb ضغط. In this sentence it means he presses or he is pressing.

The prefix يـ tells you the subject is third-person masculine singular. Arabic often uses the same form for both simple present and present progressive, so context decides whether English should be presses or is pressing.

Because the verb already includes that information. يضغط by itself already means he presses / he is pressing.

The noun صديقي is added to show who that he is: my friend. A separate pronoun like هو is usually unnecessary here unless you want extra emphasis.

Because the verb agrees with the subject, not the object.

The subject here is صديقي (my friend), which is masculine singular, so the verb is masculine singular: يضغط.

The noun القاعدة is the direct object, so its gender does not control the verb.

This is a normal verbal sentence in MSA. Arabic very often uses verb + subject + object order:

يضغط صديقي القاعدة

English usually prefers subject + verb + object, but Arabic commonly allows both patterns.

The basic noun is صديق meaning friend.

The ending ـي is an attached possessive pronoun meaning my. So:

• صديق = friend / a friend
• صديقي = my friend

That final ـي is pronounced like a long ee sound: ṣadīqī.

Because a noun with a possessive suffix is already definite.

صديقي is already specific because it means my friend, so Arabic does not add الـ to it. In other words, possession itself makes it definite here.

القاعدة is the direct object, so in full formal grammar it is accusative. In fully vowelled text, you would write it as الْقَاعِدَةَ.

In normal Arabic writing, short case endings are usually not written, so you just see القاعدة.

Also, صديقي is the subject, so it is nominative in function, but with the attached -ī suffix you do not see a separate final nominative vowel the way you do on many other nouns.

Yes. That is also grammatical.

• يضغط صديقي القاعدة = normal verbal-sentence order
• صديقي يضغط القاعدة = subject-first order, often with a bit more emphasis or topical focus on my friend

Both are possible in MSA.

A careful classroom-style pronunciation is roughly:

yaḍghaṭu ṣadīqī al-qāʿidata

At the end of a sentence, many speakers pause, so you may also hear the last word more like:

al-qāʿidah

Some tricky sounds are:

• ض = an emphatic d-like sound, written ḍ
• ص = an emphatic s-like sound
• غ = gh, similar to the French r
• ط = an emphatic t-like sound, written ṭ
• ع = ʿayn, a deep throat sound with no exact English equivalent

So يضغط is approximately yaḍ-ghaṭu, not an ordinary English-style yad-gat.