There's nothing wrong with everything being straight edge horizontal lines. However, when you want to transition from one content block to the next with a bit of style, Trims is how you do that.
To add trims to your content block, hover over it and you’ll see a toolbar appear in the upper left hand corner of that block. Click the Settings cog and a sidebar will appear.
Cycle through the different trims by using the directional arrows and when you find one you like, click "Save and Preview".
Design tip: Similar to background videos, use these with an element of caution as you don't want to go too overkill and make every content block finish with a different style of trim. Whatever style you go with, be consistent, don't mix straight edges with curved ones and stick with a theme.