دیروز یادم رفت که باید به خواهرم زنگ بزنم.

یادم رفت is a very common way to say I forgot.

Literally, it breaks down like this:

• یاد = memory / remembrance
• -م = my
• رفت = went

So the literal idea is my memory went or it slipped my mind.

This is one of the most natural everyday ways to express forgetting in Persian.

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

In this sentence, بزنم already tells us the subject is I because -م is the 1st person singular ending.

So Persian does not need من here unless you want special emphasis.

• neutral: دیروز یادم رفت که باید به خواهرم زنگ بزنم
• emphatic: من دیروز یادم رفت که باید به خواهرم زنگ بزنم

The version without من is more normal.

که here means that and introduces the clause that explains what was forgotten.

So:

• یادم رفت = I forgot
• که باید به خواهرم زنگ بزنم = that I had to call my sister

It works much like English that in I forgot that...

In Persian, که is very common for linking clauses like this.

Sometimes, but it depends on the structure.

With this exact sentence, که is natural because it introduces a full clause after یادم رفت.

However, Persian very often uses a shorter structure:

• دیروز یادم رفت به خواهرم زنگ بزنم

That means Yesterday I forgot to call my sister.

This shorter version is actually very common and often sounds more direct in everyday speech.

So:

• یادم رفت که باید... = I forgot that I had to...
• یادم رفت ... بزنم = I forgot to...

Both are correct, but the nuance is slightly different.

باید usually means must, have to, or should.

In this sentence, it gives the idea that calling the sister was something the speaker was supposed to do or needed to do.

So it is not just:

• I forgot calling my sister

It is more like:

• I forgot that I needed to call my sister
• I forgot that I was supposed to call my sister

So باید adds a sense of obligation or necessity.

بزنم is the present subjunctive form of زدن in the compound verb زنگ زدن.

After باید, Persian normally uses this kind of verb form:

• باید بروم = I must go
• باید بگویم = I must say
• باید زنگ بزنم = I must / should call

Even though the whole sentence is about the past because of یادم رفت, the clause after باید still keeps the form normally used with باید.

So the past meaning comes mainly from یادم رفت, not from changing بزنم into a past form.

Because زنگ زدن normally takes به before the person being called.

So Persian says:

• به کسی زنگ زدن = to call someone

Examples:

• به مادرم زنگ زدم = I called my mother
• به دوستم زنگ بزن = Call my friend

So به خواهرم literally means to my sister, but in natural English we just say my sister.

Yes, زنگ زدن is one of the most common ways to say to call someone on the phone.

Literally:

• زنگ = bell / ring
• زدن = to hit / strike / do

But as a compound verb, زنگ زدن means to ring or to phone.

So in modern everyday Persian, it very often means:

• to call
• to give someone a ring

Other ways to say call include:

• تلفن کردن = to telephone
• تماس گرفتن = to make contact / get in touch

But زنگ زدن is extremely common and natural.

They look the same, but they do not all do the same job.

1. یادم

Here -م is a possessive ending meaning my.

• یاد = memory
• یادم = my memory / my remembrance

2. خواهرم

Again, -م is a possessive ending meaning my.

• خواهر = sister
• خواهرم = my sister

3. بزنم

Here -م is a verb ending meaning I.

• بزنم = that I call / I should call

So:

• in یادم and خواهرم, -م = my
• in بزنم, -م = I

That is a very common thing in Persian: the same sound can have different grammatical functions.

Yes. The word order is very normal for Persian.

The sentence is:

• دیروز = yesterday
• یادم رفت = I forgot
• که باید به خواهرم زنگ بزنم = that I had to call my sister

Persian often places:

1. time expressions early in the sentence
2. the main verb near the end of its clause
3. the final verb at the end of the subordinate clause

So بزنم comes at the end because Persian is generally a verb-final language.

Also, دیروز could move, but putting it first is very natural.

Yes, you could.

For example:

• دیروز فراموش کردم که باید به خواهرم زنگ بزنم

This also means Yesterday I forgot that I had to call my sister.

The difference is mostly one of style and feel:

• یادم رفت = very natural, everyday, often sounds like it slipped my mind
• فراموش کردم = also correct and common, but a little more straightforward as I forgot

In conversation, many speakers would prefer یادم رفت.

Yes. A very common shorter version is:

دیروز یادم رفت به خواهرم زنگ بزنم.

This means:

Yesterday I forgot to call my sister.

This version removes که باید and focuses directly on the missed action.

So the difference is roughly:

• دیروز یادم رفت که باید به خواهرم زنگ بزنم
  = Yesterday I forgot that I had to call my sister.

• دیروز یادم رفت به خواهرم زنگ بزنم
  = Yesterday I forgot to call my sister.

The second one is often the more everyday phrasing.

A simple learner-friendly pronunciation is:

dirooz yâdam raft ke bâyad be khâharam zang bezanam

A few notes:

• دیروز = dirooz
• یادم = yâdam
• رفت = raft
• باید = bâyad
• خواهرم = khâharam
• بزنم = bezanam

If you say it smoothly:

dirooz yâdam raft ke bâyad be khâharam zang bezanam

That will sound quite natural.