1. Explain it simply
仅仅 means 'merely, only'. It highlights how little or how few something is.
Word order: Subject + 仅仅 + verb phrase, or 仅仅 + number + measure word.
仅仅 is more emphatic than 只; it stresses that the amount is surprisingly small.
Do not put 仅仅 at the end of the sentence.
2. Show examples
仅仅一个星期，这本书就卖了十万本。
Jǐnjǐn yī gè xīngqī, zhè běn shū jiù mài le shíwàn běn.
Sandhi:Jǐnjǐn yí gè xīngqī, zhè běn shū jiù mài le shíwàn běn.
In merely one week, this book sold a hundred thousand copies.
仅仅 + number: only one week
他仅仅是一个学生。
Tā jǐnjǐn shì yī gè xuéshēng.
Sandhi:Tā jǐnjǐn shì yí gè xuéshēng.
He is merely a student.
仅仅 before the verb 是
这个仅仅五块钱。
Zhège jǐnjǐn wǔ kuài qián.
This costs merely five kuai.
仅仅 + amount: only five kuai
3. Share a tip
仅仅 comes before the verb or the number, never at the end - say 他仅仅来了一次, not 他来了一次仅仅。