مسند الدراجة تحت هيكل الدراجة.

In Modern Standard Arabic, the present-tense verb to be is usually omitted in simple statements like this.

So:

مسند الدراجة تحت هيكل الدراجة

literally looks like:

the bicycle stand under the bicycle frame

but it naturally means:

The bicycle stand is under the bicycle frame.

If you wanted the past tense, Arabic would use a verb such as كان.

It is an iḍāfa construction, often called a construct phrase.

• مسند = stand / support
• الدراجة = the bicycle

Together, مسند الدراجة means:

• the bicycle stand
• the stand of the bicycle
• sometimes, depending on context, simply bicycle stand

English often uses of or noun-noun compounds, but Arabic commonly uses iḍāfa for this idea.

Because in an iḍāfa, the first noun usually does not take ال. The definiteness of the whole phrase comes from the second noun.

So:

• مسند الدراجة = the bicycle stand
• هيكل الدراجة = the bicycle frame

Since الدراجة is definite, the whole phrase becomes definite.

This is a very common pattern in Arabic.

Because there are really two separate iḍāfa phrases in the sentence:

• مسند الدراجة = the bicycle stand
• هيكل الدراجة = the bicycle frame

Arabic often repeats the noun like this for clarity. English might sometimes avoid repetition, but Arabic is perfectly natural here.

If the context were very clear, a pronoun could sometimes be used in a different phrasing, such as هيكلها for its frame, but the original sentence is clear and straightforward.

تحت means under or beneath.

For a learner, it is easiest to think of it as working much like a preposition:

• تحت هيكل الدراجة = under the bicycle frame

More technically, Arabic grammar often calls تحت a ظرف مكان, an adverb of place. But in simple reading, you can safely understand it as under.

For the same reason as مسند: it is the first noun in an iḍāfa.

• هيكل الدراجة = the bicycle frame

In Arabic, the first noun in an iḍāfa usually appears without ال, and the second noun shows whether the whole phrase is definite.

So even though English says the frame, Arabic says هيكل الدراجة, not الهيكل الدراجة.

With full case endings, it would be:

مِسْنَدُ الدَّرَّاجَةِ تَحْتَ هَيْكَلِ الدَّرَّاجَةِ

Here is the breakdown:

• مِسْنَدُ: nominative, because it is the main noun being talked about
• الدَّرَّاجَةِ: genitive, because it is the second part of the iḍāfa
• تَحْتَ: accusative as an adverb of place
• هَيْكَلِ: genitive in this construction
• الدَّرَّاجَةِ: genitive again, because it is the second part of the second iḍāfa

In normal pause pronunciation, many speakers will not fully pronounce all these endings.

It is a nominal sentence because it starts with a noun phrase, not a verb.

The structure is basically:

• مسند الدراجة = the topic / subject
• تحت هيكل الدراجة = the information about where it is

Nominal sentences are very common in Arabic, especially for present-tense statements like X is Y or X is in Y.

Yes, Arabic word order is somewhat flexible, but this version is the most straightforward for a learner.

مسند الدراجة تحت هيكل الدراجة
means The bicycle stand is under the bicycle frame.

Starting with مسند الدراجة makes it clear that this is the thing being described. Other orders are possible in some contexts, but this one is neutral and easy to understand.

Yes, it often can, especially when the context is clear.

More explicitly, bicycle can be:

دراجة هوائية

But in many situations, دراجة alone is enough.

This helps distinguish it from things like:

• دراجة نارية = motorcycle

So in this sentence, الدراجة naturally means the bicycle.