That it was market day I already knew very well, as the two or three main streets and wide market-place in the middle of the town were full of sheep and cows and pigs and people running about and much noise of shoutings and barking dogs.（A Traveller in Little Things by W. H. Hudson）
英文を前から読んでいくために、語句のかたまりを作ります。こんな具合に課題文をスラッシュ（斜め線）で区切ります（スラッシュリーディング）。語句のかたまりを意識すると、リスニングで英語の意味をつかむのが楽になります。
That it was market day／（主語が文頭にないときの主語の前）I already knew very well,／（接続詞の前）as the two or three main streets and wide market-place in the middle of the town／（長い主部の後）were full of sheep and cows and pigs and people running about／（接続詞の前）and much noise of shoutings and barking dogs.
語句のかたまりを前から訳していきます。
That it was market day
市が立つ日だと
I already knew very well,
すでに私にはよくわかっていた
as the two or three main streets and wide market-place in the middle of the town
なぜなら、２〜３本の大通りと、町の中心部にあって市場が開かれる広場が
were full of sheep and cows and pigs and people running about
ヒツジ、ウシ、ブタ、駆け回っている人々でごった返していたからだ
and much noise of shoutings and barking dogs.
それに、叫び声と犬の吠え声が響き渡っていた（からだ）
That it was market day I already knew very well, as the two or three main streets and wide market-place in the middle of the town were full of sheep and cows and pigs and people running about and much noise of shoutings and barking dogs.
the two or three main streets and wide market-place in the middle of the town were〜 → この部分は主部が長くなっています。どこまでが主部かわかりにくいときは、動詞の前までというのが一つの目安です。この文の場合は were の前までが主部です。
were full of → be full of =「〜で満ちている」。of とつながっているのは、sheep and cows〜だけでなく、much noise of shoutings〜もです。
That it was market day I already knew very well, as the two or three main streets and wide market-place in the middle of the town were full of sheep and cows and pigs and people running about and much noise of shoutings and barking dogs.
市が立つ日だと、すでに私にはよくわかっていた。なぜなら、２〜３本の大通りと、町の中心部にあって市場が開かれる広場がヒツジ、ウシ、ブタ、駆け回っている人々でごった返しており、叫び声と犬の吠え声が響き渡っていたからだ。
That it was market day I already knew very well, as the two or three main streets and wide market-place in the middle of the town were full of sheep and cows and pigs and people running about and much noise of shoutings and barking dogs.
今回の課題文は最初の部分が変則的な形になっており、that節から始まっています。この that節は強調のために文頭に置かれています（倒置）。
That it was market day I already knew very well→ 本来の語順は→ I already knew very well that it was market day.
動画の後半部分でリスニング用音声が流れます。
