אחי יודע להרכיב מיטה וארון, ולכן הוא יעזור לנו להרכיב גם את המדף החדש.

Because the ending ־י on a noun can mean my. So:

• אח = brother
• אחי = my brother

Hebrew often uses these attached possessive endings, especially in somewhat compact or slightly more formal style. In everyday speech, האח שלי is also very common and means the same thing.

Here it means knows how to.

When יודע is followed by an infinitive like להרכיב, it often means knows how to do something:

• יודע להרכיב = knows how to assemble

So this is not just abstract knowledge; it means he has the skill.

Also, יודע is masculine singular present tense. For a female subject, it would be יודעת.

In this context, להרכיב means to assemble or to put together.

That is the natural verb for furniture, especially things that come in parts, like:

• להרכיב מיטה = assemble a bed
• להרכיב ארון = assemble a wardrobe/cabinet
• להרכיב מדף = assemble/install a shelf

Depending on context, להרכיב can also have other meanings, but with furniture it clearly means assemble.

Because it belongs to two different verbs:

1. יודע להרכיב = knows how to assemble
2. יעזור לנו להרכיב = will help us assemble

In English, we also often repeat the verb:

• He knows how to assemble...
• He will help us assemble...

So the repetition is normal and natural.

Because את marks a definite direct object.

• מיטה וארון = a bed and a wardrobe/cabinet → indefinite
• המדף החדש = the new shelf → definite

So:

• להרכיב מיטה וארון → no את
• להרכיב את המדף החדש → את is required

A very important point: את usually is not translated into English. It is a grammar marker, not a separate meaning word.

Because in Hebrew, when a noun is definite, its adjective is usually definite too.

So:

• מדף חדש = a new shelf
• המדף החדש = the new shelf

Here:

• המדף = the shelf
• החדש = the new

The adjective חדש also matches the noun in gender and number:

• מדף is masculine singular
• so the adjective is חדש
• and because the noun is definite, the adjective becomes החדש

ולכן means and therefore, and so, or simply so.

It is made of:

• ו־ = and
• לכן = therefore / so

So the sentence is saying that because he knows how to assemble furniture, therefore he will help.

Compared with אז, לכן can sound a bit more formal or written, though it is still very common.

Yes. יעזור is the future-tense form meaning he will help.

It comes from the verb לעזור = to help.

So:

• יעזור = he will help
• תעזור = she will help / you will help
• אעזור = I will help

In Hebrew, future tense often corresponds directly to English will + verb.

Yes, it could just say יעזור.

Hebrew verbs already show person, gender, and number, so the pronoun is often optional. This sentence could also be:

• אחי יודע להרכיב מיטה וארון, ולכן יעזור לנו...

That would still be correct.

Adding הוא makes the subject a little clearer or slightly more explicit, especially after a longer first clause.

Because the verb לעזור takes the preposition ל־ in standard Hebrew.

So Hebrew says, structurally:

• לעזור לנו = help us
• literally: help to us

Examples:

• הוא עוזר לי = he helps me
• היא תעזור להם = she will help them

So לנו is exactly what you should expect after לעזור.

גם means also or too.

Here it means that he will help assemble the new shelf as well, in addition to the bed and wardrobe mentioned earlier.

So the idea is:

• he knows how to assemble a bed and a wardrobe
• therefore he will help us assemble the new shelf too

Its position before את המדף החדש is very natural. It highlights the object being added to the list of things assembled.