La profesora explica el gráfico con calma y yo comprendo mejor el tema.

Because profesora is a feminine noun meaning female teacher / professor. In Spanish, nouns referring to people often change form depending on gender:

• el profesor = the male teacher
• la profesora = the female teacher

The article changes too:

• el for masculine singular nouns
• la for feminine singular nouns

So la profesora matches a female teacher.

They match different subjects.

• la profesora explica = the teacher explains
• yo comprendo = I understand

In the present tense:

• explicar → explica for él / ella / usted
• comprender → comprendo for yo

So the verb ending changes depending on who is doing the action.

It can mean either, depending on context.

Spanish often uses the simple present where English might use either:

• The teacher explains the graph
• The teacher is explaining the graph

So La profesora explica el gráfico could describe:

• a general/habitual action, or
• something happening right now

If Spanish wants to be extra explicit about right now, it can also use:

• La profesora está explicando el gráfico

But the simple present is very common.

Spanish uses articles more often than English does.

Here you have:

• el gráfico = the graph/chart
• el tema = the topic/subject

Even when English might sometimes sound natural without the, Spanish often keeps the article. In this sentence, the speaker is referring to a specific graph and a specific topic, so el sounds completely natural.

Con calma literally means with calm, but in natural English it usually means something like:

• calmly
• slowly and carefully
• without rushing

It is a very common Spanish expression. Spanish often uses a noun phrase like this where English might prefer an adverb.

So:

• explica el gráfico con calma = she explains the graph calmly / she explains the graph in a calm way

That’s true: Spanish often omits subject pronouns because the verb ending already shows who the subject is.

So you could say:

• La profesora explica el gráfico con calma y comprendo mejor el tema.

That is grammatically fine.

But yo is included here for emphasis or contrast. It helps highlight I:

• The teacher explains the graph calmly, and I understand the topic better.

So yo is not required, but it adds a small sense of personal emphasis.

Both comprender and entender mean to understand.

In many situations, they are interchangeable:

• comprendo
• entiendo

A learner should know this:

• entender is often more common in everyday speech
• comprender can sound a little more formal or a little deeper, depending on context

In this sentence, comprendo mejor el tema sounds perfectly natural and slightly polished. It suggests I understand the topic better.

Here mejor means better, and it is working as an adverb, modifying the verb comprendo.

So:

• comprendo mejor = I understand better

Compare:

• un tema mejor would make mejor describe a noun
• comprendo mejor makes mejor describe how well the understanding happens

So it is not saying the topic is better; it is saying my understanding is better.

Because not all nouns ending in -a are feminine.

Tema is a masculine noun:

• el tema

This happens with a group of words of Greek origin ending in -ma, such as:

• el problema
• el sistema
• el programa
• el tema

So this is one of those important exceptions learners need to memorize.

Because the stress falls on the first syllable: GRÁ-fi-co.

In Spanish, words ending in a vowel, n, or s normally have stress on the second-to-last syllable. Without the accent mark, grafico would naturally be pronounced gra-FI-co.

The written accent shows that the stress is irregular:

• gráfico = GRÁ-fi-co

So the accent mark is there to show pronunciation.

Sometimes yes, but not always.

Both can mean teacher, but they are not always used in exactly the same way.

In Spain:

• profesor / profesora is very common for school teachers, especially secondary school, and also for university teachers
• maestro / maestra is often associated more with primary school teachers, or used in other special senses

So la profesora is a very normal choice here.

No, Spanish word order is more flexible than English word order, though this sentence uses a very standard order:

• La profesora
  • explica
    • el gráfico
      • con calma
• y yo
  • comprendo
    • mejor
      • el tema

This is neutral and natural.

Some parts can move for emphasis. For example:

• Con calma, la profesora explica el gráfico...
• Yo comprendo mejor el tema...

But the original version sounds clear, natural, and standard for a learner.

Y simply means and.

So:

• y yo = and I

Spanish changes y to e before words that begin with an i sound:

• padres e hijos

But yo does not begin with an i sound, so it stays:

• y yo

So y yo comprendo mejor el tema is completely correct.