Learn French: Si tu regardais le plan, nous ne serions pas désespérés. - If you looked at the map, we would not be desperate.

This sentence uses a classic si (if) clause to describe a hypothetical situation. In French, to say "If [A happened], [B would happen]", you use si + the imperfect tense for the condition, and the conditional mood for the result. That is why si tu regardais (imperfect) pairs with nous ne serions pas (conditional).

Could I use la carte instead of le plan here?

You could, but it changes the context slightly. Un plan is specifically a street map of a city, a neighborhood, or a transit system. Une carte is used for larger geographical areas like countries or regions, or for a restaurant menu! If they are lost walking around a city, le plan is the natural choice.

Why is there an -s at the end of désespérés?

Here, désespéré (desperate) acts as an adjective describing the subject nous (we). Because adjectives must agree in gender and number with the noun they describe, the plural nous requires you to add an -s. If the "we" consisted entirely of women, it would take an extra -e as well: désespérées.

How would I apply this lesson's topic to say "we wouldn't be desperate anywhere"?