First off, PC stands for Personal Computer making any computer a PC unless it's a computer in school or a library (or some other public computer ,which I just realized would still be PC).
Second, If your computer runs Windows follow these steps:
1: Right Click on your Blockland Shortcut and select properties.
2: At the end of the part that is labeled Target type: -mod editor
3: Click Apply and close that window.
4: Run Blockland from that shortcut and open up a map.
5: Press F11 to access the Mission Editor.