Iman is the main pillar of Islam, which means faith.
To have faith heart and soul in basic aspects of Islam such as belief in One Allah, His prophets & messengers and Asmani Kitabs, Angels, the Hereafter (Akhirat), Fate (Taqdir) is called Iman.
To have Faith in these basic aspects of Islam by heart, confession them by mouth and follow them in deeds is calles real Iman.
A person who sincerely believes in these things is called a Mumin/believer.
There are seven basic aspects of Iman. To be a Mumin/believer we must believe in these seven aspects.

1. Full faith in Allah
2. Belief in Angels
3. Belief in the Asmani Kitab
4. Belief in the Nabi-Rasuls of Allah
5. Belief in the Day of Judgement
6. Belief in Fate (Taqdir)
7. Belief in the life Hereafter

Kalima Tayyiba

Kalima means message or sentence. Tayyiba means sacred. Kalima Tayyiba means- sacred message, sacred sentence.

لَا اِلَهَ اِلاَّ اللهُ مُحَمَّدُ رَّسُوْ لُ الله

Pronunciation: La Ilaha Illallahu Muhammadur Rasullullah.

Meaning: There is no Mabud except Allah. Hazrat Muhammad (SM) Allah’s Rasul.

Kalima Tayyiba is the root speech of Islam. Tauhid and the oneness of Allah, and the Risalat means iman to Rasul (SM) are declared with this Kalima.

Kalima Shahadat

On the other hand, Kalima Shahadat means the sentence of giving testimony. With this Kalima we testify Tawhid and Risalat.

اَشْهَدُ اَنْ لَّا اِلَهَ اِلَّا اللهُ وَحْدَهُ لَاشَرِيْكَ لَهُ وَاَشْهَدُ اَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُوْلُه

Pronunciation: Ashhadu Al La-Illaha Illallahu Wahdahu La-Sharika Lahu, Wa Ashhadu Anna Muhammadan Abduhu Wa Rasuluhu.

Meaning: I testify that there is indeed no Deity then Allah. He is one and He has no partner. I also testify that Muhammad (SM) is Allah’s servant and messenger.

Through this Kalima we accept the Great Allah as the only Ma’bud. We testify Hazrat Muhammad (SM) as His humble servant and messenger. He is the Nabi and Rasul of Allah. We believe in Tawhid and Risalat. It is a basic acpect of Islam.
Therefore, we shall utter the Kalima correctly and act according to its inner meaning.

Iman Mujmal

اٰﻣَﻨٛﺖُ ﺑِﺎﻟﻠّٰﻪِ ﻛَﻤَﺎ ﻫُﻮَ ﺑِﺎَﺳٛﻤَﺎﺋِﻪٖ ﻭَﺻِﻔَﺎ ﺗِﻪِ ﻭَﻗَﺒِﻠٛﺖُ ﺟَﻤِﻴٛﻊَ ﺍَﺣٛﻜَﺎﻣِﻪٖ ﻭَﺍَﺭٛﻛَﺎﻧٖﻪِ

Pronunciation: Amantu billahi kama hua bi-asma-I-hi wa sifatihi wa qabiltu jamiya ahkamihi wa arkanihi.

Meaning: I believe in Allah as He is and with all His names and attributes. And I accept all of His principles and commands, laws and orders.

Iman Mufassal

اٰﻣَﻨٛﺖُ ﺑِﺎﻟﻠّٰﻪِ ﻭَﻣَﻠَﺌِﺘِﻪٖ ﻭَﻛُﺘُﺒِﻪٖ ﻭَﺭُﺳُﻠِﻪٖ ﻭَﻳَﻮٛ ﻡِ ﺍﻻٛ ﺧِﺮِ ﻭَﺍﻟٛﻘَﺪٛﺭِ ﺧَﻴٛﺮِ ﻩٖ ﻭَﺷَﺮِّ ﻩٖ ﻣِﻦَ ﺍﻟﻠّٰﻪِ ﺗَﻌَﺎﻟٰﻰ ﻭَﺍﻟٛﺒَﻌٛﺚِ ﺑَﻌٛﺪَﺍﻟٛﻤَﻮٛﺕِ

Meaning: I have Faith in Allah, His angels, His (Revealed) Books and His Rasuls (The Messengers). I also have Faith in the Day of Judgment, in the goodness and the badness of fate and in the life after death.