What does 'made for each other' means in real world?

Interesting question, Nabeha. :) I might not be able to answer it properly or as detailed (and nicely) as Zainab did, but here, few thoughts:
'Made for each other' in real life:
- Some say that couples are made in heaven. Following that logic, if they are destined for each other, there must be something in both of them that results in a perfect equation.
- When people say that a couple is 'made for each other', they usually see that equation. They realize that one's weaknesses are the other person's strength. Where one lacks, the other does not - they complement each other. However, as we know there are two rules: + and - may attract each other or + and + may attract each other as well. Some of us need a partner who has a similar mindset as we do and some of us feel attracted towards those who do not think alike.
- There is never surety if someone is the right person to spend the whole life with, but this is when 'religion' and what you expect from yourself, your life and people around you step in. It is very easy to find mistakes in other people and it is very easy to conclude that someone is no longer the right match for you. That's perhaps the most easiest way to bring a relationship to an end, because these thoughts emerge from questioning whether one is happy or not, which can be related to mood swings or comparisons (with other couples). We choose someone for us on basis of what we value most in a person. This could be his commitment to religion, his character, his education, his wealth, looks etc. Circumstances change people, but if the foundation is solid, there is, I believe not much to worry about. We need to learn and accept that 'change' is an on-going process. We keep shaping each other, since every piece of information and encounter shape us in a certain manner as well. It is important to not let negativity come near you, but instead to cherish the good moments. Of course, not every relationship works out, but there is always a purpose behind it. Those made for each other, will know how to influence the other person so that, the equation remains intact.

(P.S. could be that I drifted away from your initial question)

Honestly, I dun believe in that, there is no formula to know if a person is right for you or not in real, Have you eva heard, "no one is perfect unless you fall in love with him/her" lol. The reality is people change with time, we all do, it in human nature.. to accept that change happily is what makes a relationship work. By changing here does not mean one starts disrespecting you and not giving you that you deserve, there are few rules that we have follow. and one of them is to accept one person with all his/her positive n negative points. Unfortunately we dun do that mostly, we want other person to change for us, which is wrong, one can be flexible but can't change entirely.
And you can't say that oh see there are so good, they are made for each other bcz we dun know how much they have compromised to come at this stage. Relationships need compromise, time, communication, trust and respect, if you have it, you are good.

Akal mand kay liya ishara hee kafi hai

it feels like many people are made for me... alas i am allowed only four! :P

Made for each other is an idiom for me .... we use it for many things which are complementing each other ....

A happy marriage. ;)