Click Start Builder

Then Maximize
Now since we are working on index page you would choose home for layout.

Next is the Column (drop box).
If you want the new block to go to the left side of your page, choose Column #1

Now we passed which column the new block will go into, so now comes the Box or Block (drop down).

Im only having 2 Columns but you can set this new block for Box 3 which will give you a 3rd Column, but for this we will do Box 2.

Now since it's a new box/block, we will click the button on right side of box 3 drop down that says "New". Notice there is no info in this box/block,which means you did good and ready to go on.

Now your ready to edit this box/block and once done, click save and close Builder.

 You notice there are 2 more options on bottom, some will not know what they are for...Parameters and Custom CSS. Well for now don't worry about it, or you can Goggle the words and learn more, but we not going that deep into this subject today.

Good Luck...