2 Cor 1:4 Who comforteth us in all our tribulation, that we may be able to comfort them which are in any trouble, by the comfort wherewith we ourselves are comforted of God.
Have you been through trials or tribulations? Were you comforted of God through them? Has He led someone to you when you were in a trial that had been through it already? Has He led you to someone going through something He had brought you through already? That is how we are able to comfort others. With His help.
Here the Lord is telling us we can comfort each other through trials we all face. This is especially true if we have experienced the same type of trial. We can comfort them by showing that God led us through and will do the same for them even when things look like there is no end.
We sing this sometimes at church:
It is no secret, what God can do,
what He's done for others, He'll do for you.
With arms wide open, He'll welcome you,
It is no secret, what God can do.
Isn't that a good reminder?