Learn Spanish (Latin America): La banda corrió al escenario.

Even though a band has many members, la banda (the band) is a singular noun in Spanish. Because it functions as a single unit, we use the singular 'he/she/it' past tense ending for regular -er verbs, which is -ió. This gives us corrió.

What is the infinitive of corrió, and how does its past tense ending compare to -ar verbs?

The infinitive is correr (to run). In the past tense (the preterite), regular -er and -ir verbs share the exact same endings. For the 'he/she/it' form, that ending is -ió (corrió). This is different from -ar verbs, which just use -ó (like habló for 'he spoke'). Notice the extra i in the -er/-ir ending!

Where does al come from?

The word al is a mandatory combination of the preposition a (to) and the masculine singular article el (the). Whenever a and el are next to each other, they always merge into al. Because escenario is masculine, we say al escenario (to the stage) instead of 'a el escenario'.