How do you you write about a school schedule in Spanish?

If you want to say what number a class is, then do this:

<ordinal number> yo tengo <class name>

You can say first/second/etc in spanish:

First: primero

Second: segundo

Third: tercero

Fourth: cuarto

Fifth: quinto

Sixth: sexto

Seventh: séptimo, sétimo

Eighth: octavo

Ninth: noveno

Tenth: décimo

Class names:

Chemistry - Química

Physics - Fisica

Math - Matematicas

Geometry - Geometría

English - Inglés

Spanish - Español

Computer Science - Computacíon

So if you said "I have physics first", it would be:

Primero, yo tengo fisica.

You can also substitute in a time: e.g.

A las dos y media, yo tengo computacíon = At 2:30, I have computer science.