Inna and it's sisters

Inna and It’s Sisters
إنّ وأخواتها (inna wa-akhwātuha)

The word inna (إنَّ) is a form of emphasis (eg. “indeed” etc.) It’s used to emphasize or draw attention to something.
Example:
The house is clean. ==  .البَيْتُ نَظِيْفٌ == al-baitu nazifun
indeed, the house is clean. ==  .البَيْتَ نَظِيْفٌ انَّ== inna al-baita nazifun
The second sentence emphasizing on the house.

Effect of inna on a sentence: 

The house is clean. ==  .البَيْتُ نَظِيْفٌ == al-baitu nazifun
This is a simple nominal sentence. As we know that nominal sentence have two parts:  Subject (mubtada: مبتدا) and predicate (khabr: خبر). So البَيْتُ (al-baitu) is a subject and .  نَظِيْفٌ (nazifun) is the predicate.
After adding inna (انَّ) the subject(mubtada) is called ismu inna and the predicate (khabr) is called khabru inna. The ismu inna (mubtada) vowel case ending will change from nominative to accusative. e.g البَيْتُ (al-baitu)  will change to البَيْتَ (al-baita)
ismu inna = البَيْتَ (al-baita)
khabr inna = نَظِيْفٌ (nazifun)

The sisters of inna are follow the same rules:

لكنّ (lakinna) — but
لأنّ (li’anna) — because
كأنّ (ka’anna) — like (when you’re making a resemblance between two things)
أنَّ (anna) — similar to inna (indeed, verily, etc.)
لَعَلَّ (la’ala) — in the hope that / in the fear that (meaning depends on the context)