、、。
Every evening after school, we'd meet up in his backyard and play Indian war.
Literal
Every-evening, after-school [at-に] we [topic-は] his [genitive-の] house [genitive-の] backyard [at-で] meeting, Indian war pretend-play [object-を] did.
A nostalgic childhood scene. The standout grammar point is ごっこ — a noun-suffix attached to a noun to mean 'playing pretend at X,' 'X-game.' Common children's-play compounds: お店ごっこ (playing shop), お医者さんごっこ (playing doctor), 戦争ごっこ (playing war). It always implies make-believe, never the real activity. インディアン戦争 ('Indian war') is the kind of make-believe Western that mid-20th-century Japanese kids absorbed from American films and TV. The ~て form on 会って chains it to した ('met up and then did...'), an unbroken sequence in the past.