Learn Hardcore Japanese: syuumatu ni ribingu no yuka ni atarasii kaapetto wo sikimasita. - On the weekend I laid a new carpet on the living room floor.

Breakdown of shuumatsu ni ribingu no yuka ni atarashii kaapetto o shikimashita.

Why is there no word for “I” in this sentence? Who is doing the action?

Japanese often omits the subject when it is clear from context.

In 週末にリビングの床に新しいカーペットを敷きました。, the implied subject is usually 私 (I), or possibly we / someone in the speaker’s group, depending on the context.

If you need to be explicit, you could say:

私は週末にリビングの床に新しいカーペットを敷きました。
I laid a new carpet on the living room floor on the weekend.

But normally Japanese just leaves out 私 when it’s obvious from the situation who did it.

Why is に used after 週末? Could I say 週末で instead?

After time expressions like 週末 (the weekend), に marks the point in time when something happens:

Using で with time usually sounds wrong here. で is used more for locations or the means/way of doing something, not for simple points in time.

You can sometimes omit に after certain time words:

But 週末で新しいカーペットを敷きました is not correct for “on the weekend.”

There are two に’s: 週末に and 床に. Are they doing the same thing?