Quick Explanation:
In Spanish, we use yo for I and tú for you. The most common place we'll use them is before the verb. However, they often are used for emphasis. Sometimes people will use them after verbs, most commonly in questions or commands.

Longer Explanation:
In Spanish, we have what we call personal pronouns. In English some personal pronouns are "I" and "you". We use these before our verb or "action" to tell who does something.

So while in English we might say:

I talk with my parents.
or
You eat a lot.

I and you go before the verb and they tell you who 'talks' or who ' eats'.

Notice that in English we could not get rid of these and keep the same idea.
I talk with my parents.
It's a fact that I talk with my parents.
vs.
Talk with my parents.
I'm telling you to talk with my parents.

You eat a lot.
It's a fact that you eat a lot.
vs.
Eat a lot!
I'm telling you to eat a lot.

Spanish is much more diverse in comparison to English. If we translated those two sentences into Spanish, we would have:

(Yo) Hablo mucho con mis padres.
(I) I speak a lot with my parents.
(Tú) Comes mucho.
(You) You eat a lot

The neat thing about Spanish is that we don't have to use the yo and tú in the sentence. If you notice, the ending of our verb tells us who does the action. "Hablo" means "I talk" while "Comes" means "you eat". This makes the yo and the tú unnecessary.

What do I mean by this? Many Spanish teachers and learners explain this by saying:
In Spanish, the verb tells the story.
This is different from English where the I and you are necessary or else there is confusion.

But, we can use the yo and the tú in the sentences.

We could say:

Yo hablo con mis padres.
and
Tú comes mucho.

But the yo and tú aren't needed.

When used, they might be used for emphasis. So in a possible conversation, someone might say:

Mis amigos no hablan con sus padres, pero yo hablo con los míos.¹
My friends don't talk with their parents, but I talk with mine.
Cuando vamos al restaurante chino, yo como un poco, pero tú comes mucho.
When we go to the Chinese restaurant, I eat a little bit, but you eat a lot.

So sometimes we'll use yo and tú to emphasize someone doing the action.