How do you display all the posts with a tag from tag cloud?

Hello!

I’ve made my own theme and I’d like to have a tag cloud in the sidebar. The tag cloud is added without problems, but, when you press a tag in the tag cloud, a white page appears instead of all the posts with that tag. I don’t know what query I should use to display the posts with the tag which you pressed in the tag cloud.

I’ve spent half the day googling for an answer but found none. Please help me.

Thanks in advance!