hi,
I want to put the image filename , under the images, on album galery

On our theme's album.php add the function printImageTitle() within next_image loop I strongely recommend to read the theming tutorial for the basics.

Note that 3rd party themes (you did not say which!) may be different.

I dont understandwhat ihave to do.

Maybe it's best if you start with reading http://www.zenphoto.org/news/theming-tutorial

Did you read the theming tutorial at all?

Im reading now