Di toko olahraga, teknisi servis mengganti senar raket teman perempuan saya.

Di toko olahraga means at the sports store/shop.

• di = in / at
• toko = store / shop
• olahraga = sport / exercise

Indonesian often puts a place or time expression at the beginning to set the scene. So this sentence starts with the location first, much like At the sports store, ... in English.

You could also put it later:

Teknisi servis mengganti senar raket teman perempuan saya di toko olahraga.

That is also grammatical.

In Indonesian, the main noun usually comes first, and the word describing it comes after.

So:

• toko olahraga = sports store
  • literally: store sport

This is very common in Indonesian:

• rumah sakit = hospital
• sepatu olahraga = sports shoes
• mobil balap = race car

So toko is the main noun, and olahraga tells you what kind of store it is.

Indonesian normally does not use articles like English does.

So:

• teknisi servis can mean a service technician or the service technician
• toko olahraga can mean a sports store or the sports store

The exact meaning depends on context. Indonesian often leaves that unstated unless it really matters.

Teknisi servis means service technician, repair technician, or maintenance technician, depending on context.

• teknisi = technician
• servis = service / repair / maintenance

Servis is a loanword, ultimately from English service, but in Indonesian it often specifically refers to repair or maintenance work.

So in this sentence, teknisi servis is the person who repairs or services sports equipment.

The base word is ganti, which has the idea of change / replace.

When Indonesian makes it into an active transitive verb, it often adds the meN- prefix. Here that gives:

• ganti → mengganti = to replace

Because the subject is actively doing something to an object, mengganti is the natural form here:

• teknisi servis mengganti senar ...
• the technician replaced the strings ...

So this is a very typical Indonesian verb pattern.

The basic structure is:

• Di toko olahraga = location
• teknisi servis = subject
• mengganti = verb
• senar raket teman perempuan saya = object

So the core sentence is:

Teknisi servis mengganti senar raket teman perempuan saya.

That follows a common Indonesian pattern:

Subject + Verb + Object

This is a noun chain, and Indonesian does this a lot.

Break it down like this:

• senar = string / strings
• raket = racket
• teman perempuan saya = my female friend

So:

• raket teman perempuan saya = my female friend's racket
• senar raket teman perempuan saya = my female friend's racket string(s)

A helpful way to see the structure is:

senar [raket [teman perempuan saya]]

In more natural English, that becomes:

the string(s) of my female friend's racket

or

my female friend's racket strings

Indonesian usually shows possession just by putting nouns next to each other, with the main thing first and the owner/describer after it.

Examples:

• buku saya = my book
• rumah teman saya = my friend's house
• senar raket teman perempuan saya = my female friend's racket string(s)

So Indonesian does not need of or 's here. The relationship is understood from the word order.

Because possessors normally come after the noun in Indonesian.

Compare:

• teman saya = my friend
• teman perempuan saya = my female friend

So saya comes after the noun phrase it belongs to.

Then that whole phrase can be part of a bigger phrase:

• raket teman perempuan saya = my female friend's racket
• senar raket teman perempuan saya = my female friend's racket string(s)

This is normal Indonesian word order.

Usually it means my female friend.

• teman = friend
• perempuan = female / woman

So teman perempuan is a friend who is female.

If you want to say girlfriend in the romantic sense, Indonesian more often uses:

• pacar saya = my girlfriend / boyfriend, depending on context

So in most situations, teman perempuan saya will be understood as my female friend, not my girlfriend.

Indonesian nouns usually do not have to show singular vs. plural unless it is important.

So senar can mean:

• string
• strings

In this context, English often says the racket strings, but Indonesian can simply say senar raket and let context do the work.

If you really wanted to make it clearly plural, you could say:

• senar-senar raket

But that often sounds unnecessary. In normal Indonesian, senar raket is perfectly natural.