Learn Hardcore Spanish (Latin America): En mi escuela usamos un uniforme azul de lunes a jueves. - At my school we wear a blue uniform from Monday to Thursday.

In much of Latin America, usar uniforme is very common and completely natural.
In Spain, people tend to say llevar uniforme more often, but usar uniforme is still understood.

So usamos un uniforme azul ≈ we wear a blue uniform or we use a blue uniform (context makes it clearly “wear”).

How is usamos formed, and where is the subject we?

Usamos is the present tense, first person plural of usar (to use / to wear):

yo uso – I use
tú usas – you use (informal)
él/ella usa – he/she uses
nosotros/nosotras usamos – we use
ustedes usan – you (plural) use
ellos/ellas usan – they use

Spanish normally drops the subject pronoun when it’s clear from the verb ending.
So instead of Nosotros usamos un uniforme azul, it’s more natural to say just:

Usamos un uniforme azul – We wear a blue uniform.

The -mos ending already tells you the subject is we.

Why is it un uniforme (singular) if it means we all wear uniforms?

Spanish often uses the singular after certain verbs to talk about clothing in a general or habitual way:

Usamos uniforme – We wear a uniform (as part of the school’s rules)
Tengo coche – I have a car (not tengo coches unless you mean several)

Even though many students each have their own uniform, the idea in Spanish is “we use/wear a (type of) uniform”, not “we use/wear several uniforms”.

You could say usamos uniformes azules, but that sounds more like you are focusing on multiple physical items (for example, talking about a pile of uniforms) rather than the school rule.

Why is it un uniforme azul and not un azul uniforme?

In Spanish, most descriptive adjectives (including colors) normally come after the noun:

un uniforme azul – a blue uniform
una camisa blanca – a white shirt
unos zapatos negros – black shoes

Un azul uniforme would mean something different:

azul becomes a noun (“blue”) and uniforme becomes an adjective (“uniform, even, consistent”).
So un azul uniforme = a uniform/solid blue (color), not a blue uniform (piece of clothing).

So the normal, correct way for “a blue uniform (clothing)” is un uniforme azul.

Why is azul not plural (azules) here?

Adjectives must agree with the noun they describe, not with the idea of how many people wear it.

Noun: uniforme – singular
Adjective: azul – must be singular: uniforme azul

Plural would be:

uniformes azules – blue uniforms

In the sentence, uniforme is singular (a type of uniform), so azul stays singular.

What exactly does de lunes a jueves mean, and how is this structure formed?

de lunes a jueves means from Monday to Thursday (every week, as a habit).

Structure:

de = from
lunes = Monday
a = to
jueves = Thursday

So:

de lunes a jueves – from Monday to Thursday
de enero a marzo – from January to March

It expresses a range of days (or dates) in a concise way.

Why is there no article (el) before lunes and jueves: why not de el lunes a el jueves?

In this kind of general, habitual expression, Spanish usually drops the article:

de lunes a jueves – from Monday to Thursday (habitually, every week)

You can say:

del lunes al jueves (which is literally de + el = del, a + el = al)

But del lunes al jueves tends to refer more to a specific time period:

Voy a estar de viaje del lunes al jueves.
I’ll be traveling from Monday to Thursday (this particular week).

In your sentence (En mi escuela usamos un uniforme azul de lunes a jueves), the meaning is a regular rule, so de lunes a jueves (no articles) is the most natural.

The words lunes and jueves look singular. How do days of the week work in plural?

In Spanish, most days of the week have the same form in singular and plural:

el lunes – Monday
los lunes – Mondays
el jueves – Thursday
los jueves – Thursdays

(Only sábado and domingo change: el sábado / los sábados, el domingo / los domingos.)

So de lunes a jueves naturally covers all Mondays through all Thursdays in general, even though the words themselves don’t visibly change form.

Could I change the word order and say Usamos un uniforme azul en mi escuela?

Yes. Both are correct:

En mi escuela usamos un uniforme azul de lunes a jueves.
Usamos un uniforme azul de lunes a jueves en mi escuela.

Differences:

Starting with En mi escuela emphasizes the place (at my school…).
Starting with Usamos un uniforme azul emphasizes the action (we wear a blue uniform at my school…).

In everyday speech, both orders are natural; the original just foregrounds the school.