Oh, there's plenty of manuals around that have great step by step procedures in them. The manual for the VZ58 is in Czech, but the one for the VZ858 is translated to English. Find one of those and you'll be set.
In a nutshell though, you'll want to push in the pin holding on the gas cover (under the rear sight area), and presto that'll slip right off. The pin holds into the receiver, so don't worry about losing it. The gas piston itself is on a spring, so it's simple to get out. This is usually the dirtiest part of the gun after firing off rounds.
As for the receiver section, there's another push pin in the back of the rifle receiver area also (near the butt-stock junction with the receiver). Push that in and pull the trigger to make sure there's no tension on any of the parts (otherwise the receiver cover won't come off). After this, the cover will slip up and backward right off exposing the bolt and what not. These parts slide into and out of the receiver frame via a notched out section on the receiver, pull the bolt assembly into this section and lift it straight out. Everything else basically falls apart by hand. Remember when you're putting the gun back together that the trigger will need to be pulled again so as to get that receiver cover back on and to get the bolt assembly to fit inside those groves in the receiver's frame.