Geçen yaz sahilde her akşam yürüdüm.

Geçen yaz literally means last summer.

• geçen = past / last / previous
• yaz = summer

In Turkish, many time expressions do not need a case ending when they are used adverbially, just like English last summer, yesterday, or this morning. So geçen yaz by itself works as last summer.

The ending -de is the locative case, which usually means in, at, on depending on context.

• sahil = beach / seaside / shore
• sahilde = at the beach / on the beach / by the seaside

So sahilde tells you the location where the action happened.

Also notice consonant harmony:

• The locative ending can be -de, -da, -te, -ta
• Here it becomes -de because sahil ends in a voiced consonant and has front-vowel harmony.

Her akşam means every evening.

• her = every
• akşam = evening

Like many time expressions in Turkish, this phrase is used without a case ending when it functions adverbially. So:

• her akşam = every evening
• not her akşamda

Adding -da/-de would change the meaning and sound unnatural here.

Yürüdüm is in the simple past tense (also called the definite past in Turkish grammar).

It breaks down like this:

• yürü- = verb stem, to walk
• -dü- = past tense marker
• -m = I

So yürüdüm means I walked.

Because the subject is already built into the verb ending, Turkish does not need a separate word for I unless you want extra emphasis.

This is due to vowel harmony.

The Turkish past tense marker has four common vowel forms:

• -dı
• -di
• -du
• -dü

The verb stem here is yürü-, whose last vowel is ü, a front rounded vowel. Because of vowel harmony, the past suffix also uses ü, giving:

• yürü + düm → yürüdüm

So the form matches the final vowel pattern of the stem.

Turkish often leaves out subject pronouns when they are already clear from the verb ending.

In yürüdüm, the ending -m already means I. So:

• yürüdüm = I walked

You could say Ben geçen yaz sahilde her akşam yürüdüm, but ben would usually only be added for emphasis, contrast, or clarity.

Turkish word order is often more flexible than English, but the default neutral order tends to place the verb at the end.

This sentence is:

• Geçen yaz = time
• sahilde = place
• her akşam = frequency/time
• yürüdüm = verb

So the structure is roughly:

Last summer / at the beach / every evening / I walked

That sounds unusual in English, but it is completely natural in Turkish. The important thing is that the verb commonly comes last.

Yes, often they can.

For example, these can still work:

• Geçen yaz her akşam sahilde yürüdüm.
• Sahilde geçen yaz her akşam yürüdüm.
• Her akşam geçen yaz sahilde yürüdüm.
  This one is possible, but less neutral in everyday use.

Turkish allows movement of time and place expressions more easily than English, but the emphasis changes depending on what comes earlier. The version Geçen yaz sahilde her akşam yürüdüm is a very natural neutral sentence.

Both are possible forms, but they express different viewpoints.

• yürüdüm = I walked
  This presents the action as a completed repeated event in the past.
• yürüyordum = I was walking / I used to be walking
  This focuses more on an ongoing past action or background situation.

In Geçen yaz sahilde her akşam yürüdüm, the speaker is stating a past habit or repeated action as a fact. That is why yürüdüm works well.

If you said Geçen yaz sahilde her akşam yürüyordum, it would sound more like I would be walking every evening last summer / I used to walk every evening last summer, with a more continuous or habitual feeling.

Not exactly.

• sahil = shore, coast, seaside, waterfront, beach area
• plaj = beach, especially a beach used for swimming/sunbathing

So sahilde yürüdüm often means I walked by the seaside / along the beach / on the shore. It is a broader word than plaj.

Because of her akşam (every evening), it clearly refers to many walks, not just one.

Even though yürüdüm is a simple past form, the frequency phrase shows repetition:

• her akşam = repeatedly, every evening

So the full sentence means that during last summer, the speaker walked at the beach every evening.

Turkish often uses certain endings and common patterns to make this clear:

• Geçen yaz = time expression
• her akşam = frequency/time expression
• sahilde = place, because of the locative ending -de
• yürüdüm = action

A useful shortcut is:

• expressions with -de/-da are often locations
• bare expressions like dün, geçen yaz, her akşam are often time expressions

So even before translating, you can often tell what role each part is playing.