Mater me ad forum comitatur.

Because mater is in the nominative singular, which is the case normally used for the subject of the sentence.

• mater = mother as the doer of the action
• me = me as the person being accompanied

So mater is the one doing the accompanying.

Because me is the accusative form of the first-person pronoun, and here it is the direct object of the verb.

• ego = I (subject form)
• me = me (object form)

Since the mother is accompanying me, Latin uses me, not ego.

With comitor, the person accompanied is usually put in the accusative as a direct object. So me is exactly what we expect.

That means:

• mater me comitatur = mother accompanies me

Latin does not need cum me here, because the verb itself already carries the idea of accompanying someone.

Because comitatur is from a deponent verb.

A deponent verb:

• has passive-looking forms
• but an active meaning

So:

• comitatur looks like he/she is accompanied
• but actually means he/she accompanies

The verb is comitor, comitari, comitatus sum = to accompany.

Comitatur is:

• present tense
• indicative mood
• third person singular

So it means she accompanies or she is accompanying.

Because the subject is mater, the verb is singular: mother accompanies.

Ad forum shows motion toward a place.

• ad = to, toward
• forum = forum, marketplace
• after ad, Latin uses the accusative case
• so forum here is accusative singular

So ad forum means to the forum or toward the forum.

Because with ordinary nouns for places, Latin often uses ad + accusative to express motion toward them.

The forum is a common noun, not a city name. So Latin normally says:

• ad forum = to the forum

By contrast, with names of towns or cities, Latin often uses the accusative without a preposition.

Yes. Latin word order is much more flexible than English word order because the endings show the grammatical roles.

So all of these could mean essentially the same thing:

• Mater me ad forum comitatur.
• Me mater ad forum comitatur.
• Ad forum me mater comitatur.

The original order is straightforward and natural, but changing the order can shift emphasis.

Latin often leaves out possessive words like my when the relationship is obvious.

So mater can naturally mean:

• mother
• or, in context, my mother

Since the sentence already includes me, it is very natural to understand mater as my mother.

Mater is a third-declension noun.

Some common forms are:

• nominative singular: mater
• genitive singular: matris
• accusative singular: matrem

In this sentence, the form is mater because it is the subject.

The present tense in Latin can do either, depending on context.

So Mater me ad forum comitatur can mean:

• Mother is accompanying me to the forum
  or
• Mother accompanies me to the forum

Without more context, either a present action or a general/habitual action is possible.

Yes, depending on context, that can be a natural English translation.

The core meaning of comitor is accompany or go along with. So possible English renderings include:

• Mother accompanies me to the forum
• Mother goes with me to the forum
• Mother escorts me to the forum

The exact English choice depends on how literal or natural you want to sound.