This is the 6134th most frequent Japanese word.
オ
The Japanese character "オ" is the katakana syllable for the sound "o," used in foreign loanwords and names.
Here, 'オリンピック' refers to the Olympics, a proper noun starting with the katakana character 'オ', used for phonetic representation of foreign words.
私はオリンピックを見るのが好きです。
I like watching the Olympics.
The term 'オープン' comes from the English word 'open'. 'オ ' indicates the start of this katakana word used to represent loanwords.
そのままオープンの状態で待ってください。
Please wait with it left open.
In 'オペラを観る', the word 'オペラ' stands for 'opera', a borrowing into Japanese, used here as the direct object in the sentence.