As a set expression, さえ～ば is a combination of the 副助詞（ふくじょし） (adverbial particle) さえ, and the 接続助詞（せつぞくじょし） (conjunction particle) ば. It is used to highlight 仮定（かてい） ‘assumption’, and presents (A) as a extreme limitation that is required to achieve (B), hypothetically. This structure may be translated as ‘if only (A), then (B)’, ‘the only thing needed for (A) is (B)’, or ‘as long as (A), (B)’.
さえ may be grouped with any word, but will require the 連用形（れんようけい） (conjunctive form), or て form before it when grouped with verbs. It also regularly appears after other particles, forming a dual-particle meaning.

• この薬（くすり）を毎日（まいにち）飲（の）みさえすれば、すぐに治（なお）りますよ。
  As long as you drink this medicine every day, it will heal quickly.
• もっと若（わか）い頃（ころ）からお金（かね）を貯（た）めてさえいれば、今（いま）頃（ごろ）デカい家（いえ）を買（か）えてたかも。
  If only I had saved up money since I was young, by now, I would have been able to buy a big house.
• あの背（せ）が高（たか）い人（ひと）さえ横（よこ）にずれてくれれば、ちゃんと見（み）えるのにな。
  If only that tall person moved to the side, I would be able to see.
• タナカさんは若（わか）くさえあれば、あんな人（ひと）でも雇（やと）う。
  Tanaka-san will hire anyone, so long as they are young.
• 家（いえ）の前（まえ）の道（みち）さえ広（ひろ）ければSUVが買（か）えたのに。
  I would have been able to buy an SUV, only if the street in front of my house was bigger.
• 僕（ぼく）は静（しず）かでさえあればどこでも寝（ね）れます。
  As long as it is quiet, I can sleep anywhere.

This use of さえ is an example of 限定（げんてい） ‘limit’, with (A) being a hypothetical limit presented by the ば particle. It is also possible to see さえ with other hypothetical indicators (such as たら), but is quite rare in modern Japanese, as さえ～ば is considered a set pattern.

• バンドメンバー募集中（ぼしゅうちゅう）。ギターさえ弾（ひ）けたら誰（だれ）でもオッケーです。
  Looking for a new band member. Anyone is okay, so long as you can play the guitar.
• 日本（にほん）で英語（えいご）さえ話（はな）せたら、どこでも働（はたら）けます。
  As long as you can speak English in Japan, you can work anywhere.

This limitation is also sometimes referred to as a 条件（じょうけん） ‘stipulation’, or ‘condition’.