Learn Spanish (Latin America): Ese puente largo tiene un récord.

No, largo is a "false friend" — a word that looks like English but means something else. It actually means "long". If you want to say "large" or "big" in Spanish, you would use grande.

This lesson is about relative superlatives. How would I change this to say it's "the longest bridge"?

To make a relative superlative, you use the definite article (el or la) + más + the adjective. Because puente is a masculine noun, "the longest bridge" becomes el puente más largo. For example, you could say: Ese es el puente más largo del país (That is the longest bridge in the country).

How do I know whether to use ese or eso for "that"?

You use ese when you are describing a specific masculine noun, like ese puente (that bridge). Eso is the neutral form of "that". You only use eso when you are referring to a general idea, a situation, or an object whose name or gender you don't know yet (like asking, "What is that?").

Why does récord have an accent mark on the 'e' if it's an English word?