El telescopio usa un ocular.

• El = the
• telescopio = telescope
• usa = uses
• un = a / an
• ocular = eyepiece

So grammatically, it is a very straightforward sentence: The telescope uses an eyepiece.

Spanish uses articles very often, just like English.

• el is the masculine singular definite article: the
• un is the masculine singular indefinite article: a / an

Here:

• el telescopio = the telescope
• un ocular = an eyepiece

The article must match the noun’s gender and number, so both are masculine singular.

Because it takes the article el: el telescopio.

Also, many nouns ending in -o are masculine, though that is a pattern, not an absolute rule. In this case, telescopio is indeed masculine.

If you make it plural, it becomes:

• el telescopio → los telescopios

Usar is the infinitive, meaning to use.

In a normal sentence with a subject, you usually need a conjugated form, not the infinitive.
Here, the subject is el telescopio, which is third person singular, so usar becomes:

• yo uso = I use
• tú usas = you use
• él/ella/usted usa = he/she/you use

Since el telescopio is treated like it, the correct form is usa.

It is the present indicative.

So usa means uses or sometimes is using, depending on context. In this sentence, the most natural reading is a general fact:

The telescope uses an eyepiece.

Spanish often uses the simple present for general descriptions like this.

Spanish often leaves out subject pronouns because the verb ending already tells you the person and number.

So instead of saying: Él usa un ocular

you can simply say: Usa un ocular

In your sentence, the subject is not omitted anyway, because it is explicitly stated: El telescopio usa un ocular.

That is completely normal and natural.

Ocular is a noun here, and it means eyepiece, especially in technical or optical contexts.

For telescopes, microscopes, and similar instruments, ocular is the standard word for the part you look through.

It can also be an adjective in other contexts, meaning ocular or related to the eye, but in this sentence it is clearly a noun.

In Spain, ocular is pronounced approximately:

oh-koo-LAR

More closely:

• o as in a short Spanish o
• cu like koo
• stress on the last syllable: -lar

So: o-cu-LAR

And the full sentence is roughly: el te-les-KO-pyo OO-sa un o-ku-LAR

Because ocular is a masculine singular noun, so the correct indefinite article is un:

• un ocular = an eyepiece

You would use uno only in different situations, usually when one stands alone as a pronoun or number:

• Quiero uno. = I want one.

But before a masculine singular noun, Spanish normally uses un, not uno:

• un ocular
• un libro
• un telescopio

The standard word order here is:

Subject + verb + object
El telescopio + usa + un ocular

That is the most natural order for a neutral statement.

You could change the order in special contexts for emphasis, but for learners, the normal version is best: El telescopio usa un ocular.

Yes. Utiliza also means uses.

• usar = to use
• utilizar = to use

In many contexts, they are interchangeable.
Utilizar can sound a little more formal or technical, but both are correct.

So both of these work:

• El telescopio usa un ocular.
• El telescopio utiliza un ocular.

In this sentence, un ocular is the natural choice.

Spanish usually needs an article with a singular countable noun in this kind of statement. Since an eyepiece is a countable object, omitting the article would sound incomplete or unnatural here.

So:

• El telescopio usa un ocular. = correct
• El telescopio usa ocular. = generally not natural in this context

You would change both the noun and the articles, and the verb would agree with the new subject:

• El telescopio usa un ocular.
• Los telescopios usan oculares.

Changes:

• el → los
• telescopio → telescopios
• usa → usan
• un ocular → oculares or unos oculares, depending on meaning

Most naturally: Los telescopios usan oculares. = Telescopes use eyepieces.