Medicus artem exercet.

Because medicus is in the nominative singular, which is the case typically used for the subject.

• medicus = nominative singular
• nominative usually answers who? or what? is doing the action

So in Medicus artem exercet, medicus is the one doing the verb exercet.

Because artem is the accusative singular form of ars.

The noun is:

• ars = nominative singular, used for the subject
• artem = accusative singular, used for the direct object

Since this word is receiving the action of the verb, Latin puts it in the accusative:

• Medicus artem exercet = the doctor practices the art / skill / profession

So ars changes to artem because its job in the sentence changes.

Exercet is the 3rd person singular present active indicative of exercere.

That means:

• present = happening now
• active = the subject is doing the action
• 3rd person singular = he/she/it does it

So exercet means he practices, she practices, or it practices, depending on the subject.

With medicus, it means the doctor practices.

Because Latin usually does not need to state the subject pronoun when the verb ending already shows it.

The ending -t in exercet tells you the verb is 3rd person singular:

• exercet = he/she/it practices

Since medicus is already there as the subject, adding a separate pronoun would be unnecessary unless you wanted emphasis.

Latin has no articles. It does not have separate words for the, a, or an.

So:

• medicus can mean doctor, a doctor, or the doctor
• artem can mean art, an art, or the art

You decide from context which English article makes the most sense.

Not necessarily. Latin ars often means more than modern English art.

It can mean:

• skill
• craft
• technique
• profession
• art

In a sentence like this, artem exercere often means something like to practice one's craft/profession.

So the meaning is broader than just painting or sculpture.

Yes. Latin word order is more flexible than English because the endings show each word's role.

So these can all mean basically the same thing:

• Medicus artem exercet
• Artem medicus exercet
• Exercet medicus artem

However, word order can affect emphasis or style.

The version Medicus artem exercet is straightforward and easy for beginners:

• subject first
• object next
• verb last

That verb-last pattern is very common in Latin.

They are usually given as:

• medicus, -i = doctor
• ars, artis = art, skill
• exerceo, exercere, exercui, exercitum = practice, exercise, carry on

These dictionary forms help you identify which declension or conjugation a word belongs to and how its other forms are built.

For example:

• from ars, artis you can predict artem
• from exerceo, exercere you can recognize exercet

Because artem is the accusative singular form of ars.

If it were plural, it would be artes in the accusative plural.

So:

• artem = one art / one skill / one profession
• artes = more than one

In this sentence, the doctor is practicing one profession or craft, so the singular fits naturally.

Yes, medicus is grammatically masculine.

It normally refers to a male doctor. A feminine form would be medica.

However, when you are first learning, the main grammatical point is that medicus is a 2nd-declension masculine noun in the nominative singular.

That is why it ends in -us here.

A simple breakdown is:

• Medicus — noun, nominative singular, subject
• artem — noun, accusative singular, direct object
• exercet — verb, 3rd person singular present active indicative

So the structure is:

• subject
  • object
    • verb

That is a very common Latin pattern.