O molde é simples.

O is the masculine singular definite article, meaning the.

In o molde é simples, molde is a masculine singular noun, so it takes o:

• o molde = the mold / the template

Portuguese usually uses definite articles more often than English does, so o is very natural here.

Molde is just the dictionary form of the noun. Its grammatical gender is masculine, even though it ends in -e.

In Portuguese, noun gender is not always predictable from the ending:

• many masculine nouns end in -o
• many feminine nouns end in -a
• but nouns ending in -e can be either masculine or feminine

So you simply learn molde as a masculine noun:

• o molde
• um molde

The accent in é is important because it distinguishes this word from e.

• é = is
• e = and

So:

• O molde é simples. = The mold is simple.
• O molde e simples would be wrong

The accent also shows the stressed vowel sound.

É is the 3rd person singular present tense of the verb ser (to be).

So:

• eu sou = I am
• tu és = you are
• ele/ela é = he/she is

Here, o molde is a singular subject, so Portuguese uses é:

• O molde é simples. = The mold is simple.

Because simples is the normal Portuguese adjective meaning simple.

Even in the singular, the adjective is simples:

• o molde simples = the simple mold
• o molde é simples = the mold is simple

This adjective has the same form for masculine and feminine singular:

• o molde é simples
• a ideia é simples

Its plural form is also often written the same way in modern Portuguese:

• os moldes são simples
• as ideias são simples

So simples is a very useful adjective because it changes very little.

Because this is a normal subject + verb + adjective structure:

• O molde = subject
• é = verb
• simples = adjective describing the subject

This works like English:

• The mold is simple.

If the adjective comes directly after the noun, that creates a noun phrase instead:

• o molde simples = the simple mold

So:

• O molde é simples. = statement about the mold
• O molde simples = noun phrase, not a complete sentence by itself

A natural European Portuguese pronunciation is approximately:

u MOL-d(ɨ) eh SIM-pl(ɨ)sh

A few useful notes:

• o often sounds like u in European Portuguese when unstressed
• molde may sound roughly like MOLD with a very reduced final vowel
• é sounds like eh
• simples often ends with a sh-like sound in European Portuguese because final -s is commonly pronounced sh

So to an English speaker, the whole sentence may sound something like:

u MOLD eh SIM-plsh

That is only an approximation, but it is close enough to help.

Normally, no. In standard Portuguese, that sounds unnatural in this context.

You would usually say:

• O molde é simples.

Portuguese generally prefers the article with a noun when speaking about a specific thing. Without the article, the sentence would usually not sound complete or natural unless you are using a very special style, like headings, labels, or definitions.

The article and the verb must match the noun.

Examples:

• A forma é simples. = The shape/form is simple.
  (a because forma is feminine singular)

• Os moldes são simples. = The molds are simple.
  (os for masculine plural, são = are)

• As formas são simples. = The shapes/forms are simple.
  (as for feminine plural)

Notice that simples stays the same here.

Yes, the sentence O molde é simples. is correct and natural in both European Portuguese and Brazilian Portuguese.

The main difference is pronunciation, not grammar.

For example:

• in European Portuguese, unstressed vowels are often reduced more strongly
• in Brazilian Portuguese, vowels are usually pronounced more clearly

But the words and structure are the same.

Yes. Molde can mean things like:

• mold
• template
• pattern
• cast
• form

The exact meaning depends on context.

For example:

• in crafts or manufacturing, it may mean mold
• in sewing, it may mean pattern
• in design or documents, it may mean template

So even though the grammar is simple, the noun can be quite flexible in meaning.