When you start a new map in the editor, you are given the flag (end) and your starting block/spawn. You move the little Climbey guy to determine where players will spawn, make sure that he has a solid piece of ground underneath him, otherwise you won't be able to start the map to test it. To change the size of blocks, open your menu and spawn a block. If you are using a Vive, use the triggers to select the box (put the circle part of your controller on or inside the block and press the trigger to select it). Once selected, you can then use the arrow keys surrounding the block to increase/decrease the size of the block. To do that, you can click and drag for easier size manipulation, or you can single click to increase the size (in the direction the arrow is pointing) just a little bit. You can also rotate the blocks, look for the rotating arrows and click them to rotate the block you currently have selected. Lastly, to change the scale of the world, if you are using a vive, grab both grip buttongs and bring your controllers closer or further apart and it will scale you up or down.

Don't get discouraged, this editor is actually really intuitive once you learn the controls of it. Just play with it and experiment and you will eventually get a hang of what you need to do.

This isn't a great guide, but I hope I was able to answer your immediate question!