عندما تبدأ الحصة، يشرح المحاضر منهج الدورة.

عندما means when and introduces a time clause: عندما تبدأ الحصة = when the class begins.

It connects the first part of the sentence to the main action:

• عندما تبدأ الحصة → the time setting
• يشرح المحاضر منهج الدورة → the main action

So the structure is basically:

• When X happens, Y happens.

Because the subject is الحصة, and حصة is a feminine singular noun in Arabic.

So the verb must match it:

• تبدأ = she/it begins for a feminine singular subject
• يبدأ = he/it begins for a masculine singular subject

Since الحصة is feminine, Arabic uses تبدأ.

This is a very common Arabic word order: verb + subject.

So:

• تبدأ الحصة literally follows begins the class
• but in natural English, we translate it as the class begins

Arabic often prefers verb-first order, especially in formal writing and in clauses like this one.

You may also hear or see subject-first patterns in some contexts, but تبدأ الحصة is very normal and natural in Modern Standard Arabic.

In Arabic, the imperfect form (often called the present tense) is used not only for present actions, but also for:

• habitual actions
• repeated actions
• general truths
• future actions in some time clauses

Here the sentence describes a regular or typical sequence:

• When the class begins, the lecturer explains the course syllabus.

So the present tense gives the sense of something that regularly happens, not just one single event.

No. عندما does not normally force the verb into the subjunctive or jussive.

So the verb after it stays in its normal imperfect form:

• عندما تبدأ الحصة

That is different from particles such as لن or لم, which do change the form or ending of the verb.

Because المحاضر is the subject of the main clause, and يشرح means he explains.

So:

• يشرح = he explains
• المحاضر = the lecturer

Together:

• يشرح المحاضر = the lecturer explains

Since المحاضر is masculine singular, the verb is masculine singular too.

This is an idafa construction, often called a possessive or noun-linking structure.

In منهج الدورة:

• منهج = curriculum / syllabus
• الدورة = the course

Together, it means:

• the course curriculum
• the curriculum of the course
• the course syllabus

In an idafa:

1. the first noun usually does not take ال
2. the second noun determines whether the whole phrase is definite

So:

• منهج الدورة = the curriculum of the course
  because الدورة is definite

That is why المنهج الدورة is not correct here.

They refer to two different things:

• الحصة = the class session / lesson period
  This is the individual meeting or class period that begins.

• الدورة = the course
  This is the larger course as a whole.

So the sentence means that when one class session starts, the lecturer explains the syllabus or curriculum of the overall course.

منهج can mean method, approach, curriculum, or syllabus, depending on context.

In this sentence, because it is linked to الدورة (the course), the most natural meaning is:

• syllabus
• course outline
• curriculum

So منهج الدورة is best understood as the plan or content structure of the course.

Often, yes, but the nuance can change slightly.

• عندما is a straightforward time expression: when
• إذا can also mean when, but it often has a future or conditional flavor, something like when/if

So both can work in many situations, but عندما feels very natural for a time clause like this.

Compare:

• عندما تبدأ الحصة... = when the class begins...
• إذا بدأت الحصة... or إذا تبدأ الحصة... may sound more conditional or context-dependent, depending on style and structure

For a learner, عندما is a safe and clear choice here.

With full vowel endings, it would be:

عندما تبدأُ الحصّةُ، يشرحُ المحاضرُ منهجَ الدورةِ.

Here is why:

• تبدأُ: imperfect verb, indicative
• الحصّةُ: subject of تبدأ, so nominative
• يشرحُ: imperfect verb, indicative
• المحاضرُ: subject of يشرح, so nominative
• منهجَ: direct object of يشرح, so accusative
• الدورةِ: second term of an idafa, so genitive

In normal unvoweled Arabic writing, these endings are usually not written, but they are still understood grammatically.

A careful pronunciation would be:

ʿindamā tabdaʾu al-ḥiṣṣatu, yashraḥu al-muḥāḍiru manhaja ad-dawrati.

A simpler learner-friendly version is:

indamaa tabda'u al-hissatu, yashrahu al-muhaadiru manhaja ad-dawrati

A few pronunciation notes:

• ع in عندما is a deep throat sound with no exact English equivalent
• ح in الحصة and المحاضر is a stronger breathy h
• ص in الحصة is an emphatic s
• ض in المحاضر is an emphatic heavy consonant
• ء in تبدأ is a glottal stop, like the break in uh-oh