>I spread it in warm milk, but it came into
>>a cluster, but not dissolved at all.

The solitary problem is that your yeast did not dissolve before you added the
flour. Some brands of yeast do not dissolve easily in milk. To solve that
problem, you may either:

(1) wait longer, before adding flour; OR
(2) put the milk with yeast into a blender for a few seconds; OR
(3) dissolve the yeast in a little warm water, stir into a paste, and dissolve
that paste into the warm milk.

Neil