This is the 1215th most frequent Japanese word.
The Japanese word "twitter" (ツイッター, tsuittā) refers to the social media platform Twitter.
In this sentence, 'ツイッター' refers to the social media platform Twitter, and it is used as a noun.
私は毎日ツイッターを使っています。
I use Twitter every day.
Here, 'ツイッター' again refers to the platform, and '投稿しました' indicates the action of posting something on it.
友達が面白いツイートをツイッターに投稿しました。
My friend posted a funny tweet on Twitter.
In this sentence, 'ツイッター' is again a noun referring to the platform, and 'で' specifies the context or location of the action ('確認しています').