A mesa é baixa.

In Portuguese, it is very common to use the definite article a / o / as / os where English might or might not use the.

• a mesa = the table
• mesa by itself can sound more general, dictionary-like, or incomplete in many normal contexts.

So A mesa é baixa is the most natural full sentence for The table is low/short.

Because mesa is a feminine singular noun in Portuguese.

Portuguese nouns have grammatical gender, so the article must match:

• a mesa = the table
• o livro = the book

Here:

• a = feminine singular definite article
• mesa = feminine singular noun

Usually, you learn the noun together with its article:

• a mesa
• not just mesa

Many nouns ending in -a are feminine, and mesa is one of them. But this is not a perfect rule, so it is best to memorize nouns with their article.

É is the he/she/it form of the verb ser, which means to be.

The verb ser is used here because the sentence is describing a characteristic of the table.

• eu sou = I am
• você é = you are
• a mesa é = the table is

So é means is here.

The accent in é is important because it shows both spelling and pronunciation.

• é = is
• e = and

So the accent helps distinguish two very common words.

Because adjectives usually agree with the noun they describe in gender and number.

Since mesa is feminine singular, the adjective must also be feminine singular:

• mesa baixa = low table
• livro baixo would be masculine singular

Agreement pattern:

• baixo = masculine singular
• baixa = feminine singular
• baixos = masculine plural
• baixas = feminine plural

Yes. In Portuguese, adjectives often come after the noun.

So:

• mesa baixa = low table

That is the most normal order in this kind of sentence.

Portuguese can sometimes put adjectives before the noun, but that often changes the tone, style, or emphasis. For a basic descriptive sentence, noun + adjective is the standard pattern.

Not always. Its exact meaning depends on context.

For example, baixo / baixa can mean:

• low in height
• short for physical height in some contexts
• sometimes quiet/low with things like sound, depending on the expression

In A mesa é baixa, it most naturally describes the table’s height: The table is low.

In standard Brazilian Portuguese, baixa is pronounced approximately like BAI-sha.

A rough guide:

• bai sounds like buy
• x here sounds like sh
• final a is an open a sound

So: BAI-sha

A natural Brazilian Portuguese pronunciation is roughly:

a ME-zah EH BAI-sha

A few notes:

• mesa sounds like ME-zah
• é sounds like eh
• baixa sounds like BAI-sha

The stress is:

• MEsa
• É
• BAIxa

In most normal situations, that sounds unnatural in Portuguese.

Portuguese usually wants the article here:

• A mesa é baixa.

Leaving out the article is only possible in special contexts, headings, labels, very telegraphic style, or certain generalizations. For a normal full sentence, keep a.

The plural is:

As mesas são baixas.

Changes:

• a → as
• mesa → mesas
• é → são
• baixa → baixas

Everything agrees in number.

Normally, ser is the best choice here because the sentence describes a general characteristic of the table.

• A mesa é baixa. = The table is low.
  This sounds like a description of what the table is like.

Using estar would usually suggest a temporary state, which does not fit naturally with physical height:

• A mesa está baixa.

That would only make sense in a special context, for example if the table’s height can be adjusted and it is currently in a low position.