Firstly tribulations means suffering or trouble.
People suffer tribulations because of the consequences of their sin, let's say during your youthful age you were so arrogant or a cultist, killing someone is just a normal thing to you or disrespecting your elders or let's say how you have been living your life either as a trouble maker, an arm robber, or a prostitute.
One day it might be on your old days when you will start reaping the fruits you sowed in your youthful age, you start experiencing trouble or suffer because of the bad way you lived your life.
For some people they don't experience it, is their children that pays the price.
Maybe things will not be going well with them some people will say is because of the sin of the father.
Another one is testing from the lord. To test the faith of believers, helping them to grow in godliness and to grow deeper in God.
For example Job was put to a very hard test that took all his happiness away which coursed him to suffer, but God never left him because he is undergoing a test from the lord, but after everything he gave him more than what he Lost.
Another one is attacks from the enemy.
We also experience trouble and suffering through the attack of the enemy, the enemy doesn't want anything good to happen to us, he loves to see us believers suffer, it gives him joy, he can make believers suffer in many places like sickness, hard labor and poverty.
He might inflict us with sickness that will wash away all our money and then leave us with suffering and empty handed.
Another one is divine purpose.
Sometimes God allows us to suffer so that he will manifest himself through us, like he heals the sick, raise the dead and cast out demo's.
All this things is tribulations but God's name is exalted through the trouble and suffering.
So brethren in any tribulations you are experiencing now just trust the Lord because him alone can solve all your problems.