Learn Hardcore Japanese: ranti no ato, kigaete kara ike de booto ni norimasita. - After lunch I changed clothes and rode a boat on the pond.

ランチのあと (noun + の
- あと) sets the time: “after lunch.”
着替えてから (verb in て-form + から) means “after changing clothes.”
Combining them shows a sequence: “After lunch, and then after changing clothes, …”

What does 着替えてから literally mean, and why use the て-form of 着替える?

着替える means “to change clothes.”
Putting it in the て-form (着替えて) and adding から gives “after changing (one’s clothes).”
The て-form here links the action of changing clothes to the following action (getting on the boat).

Why is で used in 池で instead of に or を?

The particle で marks the location where an action happens.
池で means “at (or in) the pond.” It tells us where they rode the boat.

Why is に used in ボートに乗りました instead of another particle?

When you get on or enter something, Japanese uses に to mark the target of that movement.
So ボートに乗りました means “(I) got on the boat.”

Why is there no subject (like “I” or “we”) in this sentence?

Japanese often omits subjects when they’re clear from context. Here it’s understood who is eating lunch, changing, and riding the boat, so the speaker leaves it out.

Could you say 着替えたあと instead of 着替えてから, and would it change the meaning?

Yes, you could say 着替えたあと (“after I changed clothes”), which is grammatically correct. The nuance difference is subtle:

着替えたあと uses a noun form (past-tense verb + あと) and is slightly more formal or written.
着替えてから (verb て-form + から) feels more conversational and directly emphasizes “once I’d finished changing….” Both express sequence.