Pleaze can someone tell me how to get unown. A guy near veilstone told..

There is a mt near one of the towns/cities with fool of unown

Meh, go to Solaceon. Go to the right, you'll see 2 houses kinda in the woods, past them, way to the right are the Solaceon Ruins, go in there, read the Unown writings, which tells you how to get to this chamber with 4 pokeballs with items and just catch all the unown you encounter. They practically come out one by one, the different ones. Then show the little boy you meet in there your unown. You get seals to customize your pokeballs with.

Go to Solaceon and look in the ruins that are near the ledges.

Yeah.. You see, the guy near Veilstone said that too, but when I caught an Unown, he said the same thing. Nothing changed :S. Anyways, you can catch Unown from the Solaceon Ruins. It's at the right of Solaceon Town.

Go to the solaceon ruins and walk around that easy!

You get them in solaceon ruins that's all I can tell u

In Solaceon City, to the northeast, there'll be a path that leads to a cave. Some point in that cave, you'll run into some Unown.

And I'm also having trouble on how to have access to the Sinnoh Underground. I promise, once I find out, I'll let you know.

For the Unown you must go to the town that contains the day care. Once you get there, there should be a path that leads to a mountain with caves in it to the right of that town.
Once you explore those caves you should find the man and some Unown.
How to get underground? You must go to the Mining Facility in Eterna City. It should be a small house-looking building.

Hope I helped.