Problem with texture

When I click on the texture button, I have white walls... I don´t know, if that´s problem, but when I want to put there texture, I click on the image button, open, I find some .jpg and click open... But nothnig happens.. Where is problem? Must textures have some resolution or where could be problem? Thanks.

Sorry... Update: In the left part of screen I see that texture, but on the object is only white colou (I changed it to black)...

EDIT: I don´t know how, but I clicked on the replace and it works... Sorry