You need to travel into Rohan in search of what remains of the Fellowship, but for that you will need to acquire war-steeds for your companions.
'The four of you will need war-steeds if you are to have any hope of making good time on the plains of Rohan. Some of my men are returning to the Wold. You are welcome to go with them, if you like. Help my people at Langhold and Harwick, and you can have the war-steeds you need.'
You will automatically travel to Langhold in the Wold when you accept this quest.
You have travelled with some of Mansig's riders to Langhold, in the Wold, in search of war-steeds for your companions.