For example - Alt+click on world map, A context menu pops up, and gives me choices ''add marker'', ''edit marker'', ''delete marker''.
Add marker:
1. You name the marker (the name will be shown only for you when you move your mouse over the marked block)
2. You choose the color (the block you selected will be seen in the color you selected)
3. Additional info/description (like for towns, theres the town name and under it, theres a description)
4. Finish
Edit Marker:
Lets you do the same as ''Add marker'' it just edits an already existing one.
Delete marker:
Deletes the marker your mouse is currently on.
Possible uses - I mark the spot where I usually do lvling.