N4
だけで
Just by, Just with
パーティーに行くだけで楽しい。
Just going to a party is fun.
Explanation
「〜だけで」 says that this one thing alone is enough to bring about the result, or to make the following possible: 「名前を書くだけでいいです」 (Just writing your name is fine), 「彼女の声を聞くだけで元気になる」 (Just hearing her voice cheers me up). It often carries a feeling of 'it's easy, no extra effort' or 'a tiny stimulus brings a strong reaction'.
Mixed up with
「〜だけでなく」 means 'not only …', and what follows usually goes a step further: 「言葉だけでなく、行動も大切だ」 (Not only words, actions matter too).
「〜だけでは〜ない」 means '… alone is not enough': 「努力するだけでは成功できない」 (Effort alone won't bring success).
To say 'all you need is …', Japanese often uses 「〜だけでいい」, which is more direct than 「〜ばいい」.