Learn Spanish (Latin America): Abrí el capó y volví a armar el motor. - I opened the hood and assembled the engine again.

The structure volver a + infinitive is the most natural way in Spanish to say you did an action again. Instead of adding a phrase like otra vez at the end of the sentence, you conjugate volver and follow it with a and the action verb. Here, volví is the past tense (preterite) for "I", so volví a armar means "I assembled again."

Does armar have something to do with weapons or armies?

It can, as it literally translates to "to arm" in a military context. However, in everyday Latin American Spanish, armar is the standard verb for "to put together" or "to assemble." You use it for building engines, putting together furniture, or assembling a jigsaw puzzle.

Why are both abrí and volví in the preterite past tense, rather than the imperfect?

These are single, completed actions that happened one right after the other. The speaker opened the hood (first completed action) and then put the engine back together (second completed action). A chain of consecutive events in the past always uses the preterite tense to move the story forward.

Is el capó the only word for a car's hood?