Learn Spanish (Latin America): Llego temprano en metro.

In English we say "by subway," but Spanish uses the preposition en for almost all modes of transportation. You can think of it as traveling "in" the vehicle. You will use this same pattern for things like en coche (by car) and en tren (by train).

Why is it just en metro and not en el metro?

When you use en to talk about a mode of transportation, you generally do not use a word for "the" (el or la). Just like in English we say "by subway" and not "by the subway," Spanish simply uses en metro.

Where is the word for "I" (yo) in this sentence?

The word yo (I) is hidden inside the verb! In Spanish, the -o ending of llego already tells you that "I" am the one arriving. You could say yo llego, but it is completely normal and more common to just drop the yo.

What is the base verb for llego?

The base form of the verb is llegar, which means "to arrive." Because it is a regular verb that ends in -ar, you drop the -ar and add -o to talk about yourself doing the action.