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.
As long as you drink this medicine every day, it will heal quickly.
If only I had saved up money since I was young, by now, I would have been able to buy a big house.
If only that tall person moved to the side, I would be able to see.
Tanaka-san will hire anyone, so long as they are young.
I would have been able to buy an SUV, only if the street in front of my house was bigger.
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.
Looking for a new band member. Anyone is okay, so long as you can play the guitar.
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’.