How did general mcclellan move his troops to virginia?

In July 1861, President Lincoln asked McClellan to train and build the main force of the union army.George McClellan was the major general in the Union army.On march of 1862, McClellan Potomac army began moved towards the capital of the confederate but soon the spring season rain turned the dirt roads into rivers of mud.Due to this McClellan man could not walk properly, walking speed reduced and they could not bring their heavy machine guns with them.but soon Union army artillery arrived since its placed Confederates troops already withdrawn and hide near the woods of Williams-burg.