All three words look very similar. So watch out and don’t mix them up.
Here is a list what they mean and how they are used:
when; as suddenly
إذا is normally introducing a conditional sentence.
The verbal sentence (جُمْلة فِعْلِيّة) after it is usually in the past tense – but it has the meaning of the present tense or even future tense!
Notice: The word إِذا can only be used if the situation in the conditional sentence can theoretically be achieved, if it is possible, or has happened. This is different to إنْ – as the word إنْ can be used for introducing a possible or impossible condition, as shown in the examples below.
If you are successful in your work, you will be successful in your life. (This leaves open if you are successful or not; you could be both.)
إنْ تَجْتَهِدْ في عَمَلِكَ تَنْجَحْ في حَياتِكَ
When the sun rises (and the sun does rise every day without an exception) people will go to their work.
إذا طَلَعَتْ الشَّمْس ذَهَبَ النَّاسُ إلى عمالِهِم
as; when; since; as; because
It can be used as a causal or temporal conjunction. Normally, a verbal sentence (جُمْلة فِعْلِيّة) in the past follows, very rarely you see a nominal sentence (جُمْلة اِسْمِيّة). It has usually the meaning of عِنْدَ ما
She cried as she was sick.
بَكِيَتْ إذْ كانَتْ مَرِيِضةً
then; therefore; hence; that’s why; consequently; in that case
إذًا = إذَنْ
Often used in a dialogue in response to what was said before.
A: We will meet at the centre.
سَنَلْتَقي في الْمَرْكَزِ
B: Let’s have a coffee together then.
إذَنْ نَشْرَبُ قَهْوى مَعًا