Step 1. Get the free version of Fraps.
Step 2. Start Fraps, then start Blockland.
Step 3. Host a server where you say that you're filming whatever.
Step 4. Make a bunch of video clips and save then to a folder entitled "Blockland Movies (I hope you know how to make folders)
Step 5. Put all your clips into some sort of editing tool and edit it however you want. (ex. add credits, music, etc.)
Step 6. Save completed version somewhere.