A mobília de que precisamos é simples: uma mesa, duas cadeiras e uma cama.

Because mobília is a collective noun: it refers to furniture as a group, not to one single object.

So even though the sentence later mentions a table, two chairs, and a bed, the grammatical subject is still a mobília = the furniture, which is singular.

This is similar to English furniture, which is also grammatically singular:

• The furniture is simple
• not The furniture are simple

The article A means the, so A mobília means the furniture.

Portuguese uses definite articles very naturally when talking about a specific thing already identified by the rest of the sentence. Here, it is not furniture in general, but the furniture that we need.

So:

• mobília = furniture, as a general concept
• a mobília de que precisamos = the furniture that we need

Portuguese often uses articles more freely than English does.

All three can relate to furniture, but they are not used in exactly the same way.

• mobília = furniture / furnishings as a set
• móveis = pieces of furniture, literally furniture items
• mobiliário = furniture/furnishings, often a little more formal or technical

In everyday European Portuguese, móveis is very common when talking about actual items:

• Precisamos de poucos móveis.

Mobília is perfectly correct here and sounds natural, especially when referring to the set of furniture needed for a place.

Because the verb precisar normally takes the preposition de in standard Portuguese:

• precisar de alguma coisa = to need something

So:

• Precisamos de uma mesa. = We need a table.

When that noun becomes part of a relative clause, the de must stay:

• a mobília de que precisamos

Literally, this is something like:

• the furniture of which we need but in natural English we simply say:
• the furniture that we need

English often leaves the preposition at the end or drops it in this kind of structure, but Portuguese normally keeps it before the relative pronoun.

Yes. A mobília da qual precisamos is grammatically correct.

Both are correct:

• de que precisamos
• da qual precisamos

The difference is mainly style:

• de que is very common and natural
• da qual sounds a bit more formal or heavier

For most learners, de que is the more useful everyday pattern to remember.

Because standard Portuguese does not normally leave the preposition at the end of the clause the way English can.

English allows:

• the furniture that we need
• the furniture which we need
• and even structurally the furniture that we need for the house

But in Portuguese, if the verb needs de, that preposition usually has to come before the relative word:

• a mobília de que precisamos
• a mobília da qual precisamos

So que precisamos de is not the standard structure here.

There are two separate points here.

1. Why is it é? Because the subject is singular: A mobília.

So:

• A mobília é simples.
• not A mobília são simples.

2. Why does simples end in -s? Because some Portuguese adjectives have the same form in the singular and the plural. Simples is one of them.

Examples:

• uma solução simples
• duas soluções simples

So simples does not become singular just by losing the -s. Its form stays the same.

Because Portuguese normally uses an article or determiner with each countable noun in a list like this.

Here:

• uma mesa = a table
• duas cadeiras = two chairs
• uma cama = a bed

Notice that duas is the feminine form of two, because cadeiras is feminine plural.

This kind of listing is very normal in Portuguese:

• um sofá, uma mesa e quatro cadeiras
• duas janelas e uma porta

The colon introduces an explanation or a list.

The sentence first gives the general idea:

• A mobília de que precisamos é simples

Then, after the colon, it specifies what that simple furniture consists of:

• uma mesa, duas cadeiras e uma cama

So the colon works like:

• namely
• that is
• as follows

In European Portuguese, mobília is pronounced roughly like moh-BEE-lya, with the stress on bí.

A helpful breakdown is:

• mo-BÍ-lia

A few pronunciation notes:

• the stressed syllable is clearly marked by the accent: í
• the final -ia is not pronounced like English eye-uh; it is more compact
• in European Portuguese, unstressed vowels are often reduced, so the first syllable may sound weaker than an English speaker expects

So if you want a practical learner version, moh-BEE-lya is a good approximation.