Learn Spanish (Latin America): Tú lees el libro.

In Spanish, you can often drop the subject pronoun because the verb ending already tells us who is doing the action. Saying Lees el libro is perfectly correct and very common. Including Tú here just adds a little emphasis.

Does Spanish always use this Subject-Verb-Object word order?

For basic statements like this one, yes! Spanish uses the exact same Subject-Verb-Object structure as English: Tú (subject) lees (verb) el libro (object).

How would I make this sentence negative?

To make a sentence negative in Spanish, you simply put the word no right in front of the verb. The negative version is Tú no lees el libro. Notice that Spanish doesn't use a helper word like the English word "do".

Why does the verb lees end in an s?

Spanish verbs change their endings to match the person doing the action. The dictionary form of this verb is leer (to read). When you are talking to someone using tú (you, informal), regular verbs that end in -er drop that ending and add -es, making it lees.