This feature helps you ensure that all elements are aligned vertically, and horizontally. To start, in the Design editor, select all the elements you want to align. To select multiple elements, hold the Shift key while selecting them.

Once all elements are selected, the alignment buttons will show up below the slide. You can hover over each button to read its tooltip.

Before aligning elements to Top, for example, make sure to position the highest element where you want the rest to be aligned. Same for aligning to Bottom.

Use the grid on the background to manually adjust the alignment when needed. You can undo unwanted alignments using Ctrl+Z.