המכשיר החדש קטן, אבל הוא מהיר יותר מהמכשיר הישן.

In Hebrew, descriptive adjectives usually come after the noun.

So:

• המכשיר החדש = the new device
• literally: the device the-new

This is the normal Hebrew word order for noun + adjective. The same thing happens in:

• המכשיר הישן = the old device

Because when a noun phrase is definite in Hebrew, the adjective normally becomes definite too.

So:

• מכשיר חדש = a new device
• המכשיר החדש = the new device

Likewise:

• מכשיר ישן = an old device
• המכשיר הישן = the old device

This is different from English, where only the appears once.

Because קטן here is not part of the noun phrase the new device. It is the predicate adjective: is small.

Compare these two patterns:

• המכשיר הקטן = the small device
  Here קטן is part of the noun phrase, so it becomes definite: הקטן.

• המכשיר קטן = the device is small
  Here קטן is describing the subject in the sentence, so it does not take ה־.

In your sentence:

• המכשיר החדש קטן = the new device is small

So החדש is attributive, but קטן is predicative.

In present-tense Hebrew, the verb to be is usually omitted.

So Hebrew often says:

• המכשיר החדש קטן
• literally: the new device small

but the meaning is:

• The new device is small

This is completely normal.
In past or future, Hebrew does use forms of to be, for example:

• המכשיר היה קטן = the device was small
• המכשיר יהיה קטן = the device will be small

הוא is the pronoun he / it.

Since מכשיר is a masculine singular noun, Hebrew refers back to it with the masculine singular pronoun:

• הוא = he / it

For objects, English uses it, but everyday Hebrew does not have a separate neuter pronoun. So masculine or feminine pronouns are used according to the noun’s grammatical gender.

Here:

• אבל הוא מהיר יותר... = but it is faster...

Hebrew usually forms comparisons with:

• adjective + יותר + מ־

So here:

• מהיר = fast
• יותר = more
• מ־ = than / from

Together:

• מהיר יותר מהמכשיר הישן
• literally: fast more than the old device
• natural English: faster than the old device

Unlike English, Hebrew does not usually add -er to the adjective.

Because Hebrew prepositions are often written as prefixes attached to the following word.

Here, מ־ means from or, in comparisons, than.

So:

• מ־ + המכשיר
• becomes מהמכשיר

That whole phrase means:

• than the device
• or literally from the device

In comparison sentences, מ־ is the normal way to say than.

Because מכשיר is a masculine singular noun, and Hebrew adjectives agree with the noun they describe.

So you get masculine singular forms:

• חדש
• קטן
• מהיר
• ישן

If the noun were feminine, the adjectives would change too. For example, with מכונה (machine, feminine), you would expect forms like:

• חדשה
• קטנה
• מהירה
• ישנה

Yes, often it could, if the context is clear.

For example, a speaker might say:

• אבל הוא מהיר יותר מהישן
• but it is faster than the old one

But מהמכשיר הישן is fuller and more explicit. It can sound clearer, especially in writing or when you want to avoid any ambiguity.

A simple transliteration is:

ha-makhshir he-khadash katan, aval hu mahir yoter meha-makhshir ha-yashan

A few pronunciation notes:

• kh represents the throaty Hebrew sound in letters like ח
• stress is usually near the end:
  • makhSHIR
  • khaDASH
  • yaSHAN

A natural English-style approximation is:

ha-makh-SHEER he-kha-DASH ka-TAN, a-VAL hoo ma-HEER yo-TER me-ha-makh-SHEER ha-ya-SHAN