It is really hard. Incredibly hard.
Part of the reason why the USA has such a dominant military is because it has built incredibly long and sturdy supply chains that can move soldiers and materiel around the world quickly to soldiers.
First, you need to get this to the front, which usually requires a supply chain, reserves, and a manufacturing base to replenish reserves. Russia's economy is ok, but this is the first war in a generation and the Russian economy is showing obvious cracks in being able to supply soldiers. You also have Ukraine getting its supplies from the best logistics force in the world and its economic allies.
Second, you need to actually deploy the resources to the front. That usually requires competent military logistics being able to move these supplies. If your logistics people are corrupt or incompetent, that may not happen to the volumes needed.
So, yeah, there appears to be logistics problems with the Russian military.