The set phrase さえ～ば is formed by pairing the adverbial particle さえ with the conditional particle ば. It is used to express a hypothetical situation where (A) is presented as the one and only condition that needs to be met for (B) to happen. This can be translated into English as 'if only (A), then (B)', 'as long as (A), (B) will happen', or 'all that's needed for (B) is (A)'.

さえ can follow most types of words. However, when it is used with a verb, the verb must first be changed to its conjunctive form, or て-form. It is also quite common to see さえ come after another particle, giving it a dual-particle function.

• ピアノは、ちゃんと練習(れんしゅう)しさえすれば、上手(じょうず)になりますよ。
  When it comes to the piano, as long as you practice properly, you will get good at it.
• もっと真面目(まじめ)に勉強(べんきょう)してさえいれば、いい大学(だいがく)に入(はい)れたかもしれない。
  If only I had studied more seriously, I might have been able to get into a good university.
• この鍵(かぎ)さえあれば、部屋(へや)に入(はい)れるのに。
  If only I had this key, I could get into the room.
• そのジャケットは、安(やす)くさえあれば、どんなデザインでも買(か)います。
  I'll buy that jacket in any design, so long as it's cheap.
• 天気(てんき)さえ良(よ)ければ、昨日(きのう)のハイキングは楽(たの)しかったのに。
  Yesterday's hike would have been fun, if only the weather had been better.
• 私(わたし)は料理(りょうり)が簡単(かんたん)でさえあれば、毎日(まいにち)作(つく)ります。
  As long as the dish is easy to make, I'll cook every day.

This usage of さえ illustrates a limit, where the ば particle introduces (A) as the one hypothetical requirement. While it is technically possible to pair さえ with other conditional forms (like たら), it is uncommon in contemporary Japanese because さえ～ば has become a standard, fixed expression.

• アルバイト募集(ぼしゅう)！パソコンさえ使(つか)えたら誰(だれ)でも歓迎(かんげい)です。
  Part-time job opening! Anyone is welcome, as long as you can use a computer.
• お金(かね)さえあったら、世界中(せかいじゅう)を旅行(りょこう)できます。
  As long as you have money, you can travel anywhere in the world.

This limiting function is sometimes also called setting a 'stipulation', or 'condition'.