How do you merge by distance in Blender Edit Mode?

In Blender Edit Mode, you merge vertices by distance using the "Merge by Distance" option. Here's how:

1. Enter Edit Mode: Select your object and press Tab to switch to Edit Mode.
2. Select Vertices: Select the vertices you want to merge. You can use box select (B), circle select (C), or individual selection. To select all vertices, press A.
3. Merge Menu: Press M to bring up the Merge menu.
4. Choose By Distance: Select "By Distance" from the Merge menu.
5. Adjust Threshold (if needed): A small pop-up in the lower-left corner of the 3D Viewport will appear. This allows you to adjust the Merge Distance. Vertices within this distance of each other will be merged into a single vertex. If you don't see it, expand the small arrow at the bottom left of your viewport. If no vertices are merged, increase the Merge Distance.

The bottom of the viewport will display a message indicating how many vertices were removed after the merge operation is complete (e.g., "Removed 5 vertices").