First they are using infantry to move through the massive minefields and are leaving their tanks and heavy equipment behind, working at night, which means the Russians don't have proper night vision capabilities or flares to light up the battlefield, though, of course these are merely details in the Ukrainian narrative.
Secondly they have succeeded in destroying most of the Russian artillery, command posts, logistics and supply lines, behind the actual lines of fortifications.
As far as I can see, all these stories have only one source, the Ukrainians themselves. There is absolutely no independent or neutral verification of any of this, at all. No western journalists have been allowed anywhere near the actual frontline to examine the veracity of the Ukrainian claims to substantial military success, a turning point in the war.