Bu yöntem başarısız olursa, başka bir plan yapmalıyız.

Olursa means if it happens / if it becomes / if it is in this context.

It comes from olmak = to be / to become / to happen.

Here, başarısız olursa is a very natural Turkish way to say:

• if it fails
• if it is unsuccessful

So the sentence uses başarısız olmak literally as to be/become unsuccessful.

It can be broken down like this:

• ol- = verb stem from olmak
• -ur- = aorist/general tense marker
• -sa = conditional marker, meaning if

So:

• olur = it is / it becomes / it happens
• olursa = if it is / if it becomes / if it happens

In this sentence, it is third person singular, so the subject is understood as bu yöntem.

Turkish often expresses this idea with an adjective plus olmak:

• başarısız = unsuccessful
• başarısız olmak = to be unsuccessful / to fail

So instead of one single verb like English fail, Turkish commonly uses this structure.

You may also hear other ways to express failure in different contexts, but başarısız olmak is very common and neutral.

Başarısız means unsuccessful.

It comes from başarı = success, plus -sız, which means without.

So literally:

• başarı = success
• başarısız = without success = unsuccessful

This -sız / -siz / -suz / -süz pattern is very common in Turkish.

Examples:

• tuz = salt → tuzsuz = unsalted / without salt
• umut = hope → umutsuz = hopeless

Because Turkish usually includes the subject inside the verb ending.

Yapmalıyız already means we should/must do/make.

It breaks down like this:

• yap- = do / make
• -malı = should / must
• -yız = we are / we

So the we is built into the verb.
You could add biz for emphasis:

• Biz yapmalıyız = We should do it

But normally it is not necessary.

Yapmalıyız means we should make/do or we must make/do, depending on context.

The suffix -malı / -meli expresses necessity, obligation, or strong advice.

So başka bir plan yapmalıyız can mean:

• we should make another plan
• we need to make another plan
• we must make another plan

In this sentence, should or need to is often the most natural English translation.

That y is a buffer consonant.

The form is basically:

• yapmalı
  • -ız

But Turkish often inserts y between vowels to make pronunciation smoother:

• yapmalıız → yapmalıyız

This happens a lot in Turkish when suffixes come together.

Başka bir plan means another plan or a different plan.

• başka = other / another / different
• bir = a / one

Together, they naturally mean another.

So:

• başka plan can sometimes work in certain contexts
• but başka bir plan is the most natural way to say another plan

Because plan here is an indefinite direct object.

In Turkish, direct objects are often:

• without accusative if they are indefinite/non-specific
• with accusative if they are definite/specific

So:

• başka bir plan yapmalıyız = we should make another plan
  indefinite, so no accusative

Compare:

• planı yapmalıyız = we should make/do the plan
  specific plan, so accusative -ı

Turkish often puts the if clause before the main clause, just like English often does:

• Bu yöntem başarısız olursa, başka bir plan yapmalıyız.

This is very natural and common.

Turkish word order is somewhat flexible, so other orders are possible for emphasis, but this version is the most neutral and standard.

Yes.

Because başarısız olursa literally leans toward if it is/becomes unsuccessful, but in natural English that is often simply:

• if this method fails

Both are good translations. The difference is mostly about what sounds natural in English, not a big grammatical difference in Turkish.

Bu yöntem means this method or this approach.

• bu = this
• yöntem = method

It is the subject of başarısız olursa.

So the first part literally works like:

• this method if it fails / if this method is unsuccessful

Then the second part gives the result:

• başka bir plan yapmalıyız = we should make another plan

Yes. Very often, Turkish expresses if by adding the conditional suffix -sa / -se directly to the verb.

Examples:

• gelirse = if he/she comes
• yağarsa = if it rains
• olursa = if it happens / if it is

So in this sentence, Turkish does not need a separate word exactly like English if. The idea of if is built into olursa.