What can you do with the elder scroll after ive killed alduin?

You talk to the bridge guard and return to Skyrim. That is essentially the end of the main quest line. However, there are several other story arcs to be explored. The Thieves Guild, College of Winterhold, Dark Brotherhood, The Companions, The Skyrim Civil War.
If you have the Dragonborn and Dawnguard DLC, you can also follow their main quest lines.
And once you have completed everything that vanilla Skyrim has to offer, you can install mods like Moonpath to Elswyr, Falskaar, The Forgotten City, Project AHO, and Beyond Skyrim, some of which add entire regions to the game.